@timo I did. I can't figure out where it's finding that .0 it adds to the 1883 port I have in the cfg-file

Did that, MQTT bridge stuck at "initializing". Not the full answer yet, but thanks @timo for your effort!

Openhab.log when I checked the Services - MQTT in Paper UI

2018-06-08 00:59:19.162 [ERROR] [rotocol.mqtt.MySensorsMqttConnection] - MQTT connection offline - Reason unknown
2018-06-08 00:59:19.221 [WARN ] [me.config.core.internal.ConfigMapper] - Could not set field value for field 'port': For input string: "1883.0"
java.lang.NumberFormatException: For input string: "1883.0"
	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) ~[?:?]
	at java.lang.Integer.parseInt(Integer.java:580) [?:?]
	at java.lang.Integer.valueOf(Integer.java:766) [?:?]
	at org.eclipse.smarthome.config.core.internal.ConfigMapper.objectConvert(ConfigMapper.java:159) [98:org.eclipse.smarthome.config.core:0.10.0.oh230]
	at org.eclipse.smarthome.config.core.internal.ConfigMapper.as(ConfigMapper.java:98) [98:org.eclipse.smarthome.config.core:0.10.0.oh230]
	at org.eclipse.smarthome.config.core.Configuration.as(Configuration.java:54) [98:org.eclipse.smarthome.config.core:0.10.0.oh230]
	at org.eclipse.smarthome.io.transport.mqtt.internal.MqttBrokerConnectionServiceInstance.modified(MqttBrokerConnectionServiceInstance.java:77) [207:org.eclipse.smarthome.io.transport.mqtt:0.10.0.oh230]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:?]
	at org.apache.felix.scr.impl.inject.BaseMethod.invokeMethod(BaseMethod.java:229) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.inject.BaseMethod.access$500(BaseMethod.java:39) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.inject.BaseMethod$Resolved.invoke(BaseMethod.java:650) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.inject.BaseMethod.invoke(BaseMethod.java:506) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.inject.ActivateMethod.invoke(ActivateMethod.java:307) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.inject.ActivateMethod.invoke(ActivateMethod.java:299) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.manager.SingleComponentManager.invokeModifiedMethod(SingleComponentManager.java:772) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.manager.SingleComponentManager.modify(SingleComponentManager.java:727) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.manager.SingleComponentManager.reconfigure(SingleComponentManager.java:645) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.manager.SingleComponentManager.reconfigure(SingleComponentManager.java:609) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.manager.ConfigurableComponentHolder.configurationUpdated(ConfigurableComponentHolder.java:426) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.manager.RegionConfigurationSupport.configurationEvent(RegionConfigurationSupport.java:284) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.scr.impl.manager.RegionConfigurationSupport$1.configurationEvent(RegionConfigurationSupport.java:89) [41:org.apache.felix.scr:2.0.12]
	at org.apache.felix.cm.impl.ConfigurationManager$FireConfigurationEvent.sendEvent(ConfigurationManager.java:2090) [8:org.apache.felix.configadmin:1.8.16]
	at org.apache.felix.cm.impl.ConfigurationManager$FireConfigurationEvent.run(ConfigurationManager.java:2058) [8:org.apache.felix.configadmin:1.8.16]
	at org.apache.felix.cm.impl.UpdateThread.run0(UpdateThread.java:141) [8:org.apache.felix.configadmin:1.8.16]
	at org.apache.felix.cm.impl.UpdateThread.run(UpdateThread.java:109) [8:org.apache.felix.configadmin:1.8.16]
	at java.lang.Thread.run(Thread.java:748) [?:?]
2018-06-08 00:59:19.340 [WARN ] [.MqttBrokerConnectionServiceInstance] - Ignore existing broker connection configuration for: mosquitto```

Help!
I semi-followed this thread but also built a shield like this:
http://www.instructables.com/id/Arduino-UNO-as-AtMega328P-Programmer/

For the Uno, the ArduinoISP sketch goes fine. After that, I connect the shield and 328p and upload stuff.
Since my build has 3.3V regulated power (using PCB My Slim 2AA Battery Node..but I can sneak wires to it easily so no need for batteries), I selected 'Board -> Pro Mini' and type '3.3V 8Mhz'. Burn bootloader goes fine, no errors. Upload sketch using programmer (Arduino as ISP) also uploads fine.
When I plug it in (USB FTDI-clone 3.3V selected) and see serial monitor, it remains blank. Nor does the node work when plugged into power.

Anybody else try this? Ideas? The slim node has all caps and resistor connected.

EDIT:
I used the recommended board download from 8Mhz instructions and bingo, it's working...partly. Have to check radio wiring.
Should just follow instructions and not go off on my own......

Great instructions, thanks!
My problems started yesterday with my OpenHab2 updating to 2.3.0.

I'm using Rpi Zero W / DietPi - conf to MQTT gw. Mosquitto and mysgw service work OK. Everything else doesn't.
My problems briefly from the logs:

1527624943: New client connected from 127.0.0.1 as mygateway1 (c1, k15, u'masi').
1527626485: New connection from 127.0.0.1 on port 1883.
1527626485: New client connected from 127.0.0.1 as mosqsub/3760-DietPi (c1, k60, u'masi').
1527626499: Socket error on client mosqsub/3760-DietPi, disconnecting.

OpenHab (edited):

2018-05-29 23:17:17.655 [DEBUG] [org.openhab.binding.mysensors       ] - BundleEvent STARTING - org.openhab.binding.mysensors
2018-05-29 23:17:17.880 [DEBUG] [org.openhab.binding.mysensors       ] - BundleEvent STARTED - org.openhab.binding.mysensors
2018-05-29 23:17:18.019 [DEBUG] [org.openhab.binding.mysensors       ] - ServiceEvent REGISTERED - {org.eclipse.smarthome.core.thing.binding.ThingHandlerFactory}={service.id=116, service.bundleid=13, service.scope=bundle, component.name=org.openhab.binding.mysensors.factory.MySensorsHandlerFactory, component.id=15} - org.openhab.binding.mysensors
2018-05-29 23:19:24.908 [WARN ] [lipse.smarthome.io.net.exec.ExecUtil] - Execution failed (Exit value: -559038737. Caused by java.io.IOException: Cannot run program "arping" (in directory "."): error=2, Tiedostoa tai hakemistoa ei ole)
2018-05-29 23:19:25.184 [INFO ] [ternal.dhcp.DHCPPacketListenerServer] - DHCP request packet listener online
2018-05-29 23:19:25.985 [DEBUG] [nsors.handler.MySensorsBridgeHandler] - Initialization of the MySensors bridge
2018-05-29 23:19:26.257 [DEBUG] [ensors.factory.MySensorsCacheFactory] - Cache file: given_ids.cached exist.
2018-05-29 23:19:26.315 [DEBUG] [ensors.factory.MySensorsCacheFactory] - Cache (given_ids) content: [0, 1, 99, 4, 5]
2018-05-29 23:19:26.594 [DEBUG] [rotocol.mqtt.MySensorsMqttConnection] - Enabling connection watchdog
2018-05-29 23:19:26.795 [ERROR] [rotocol.mqtt.MySensorsMqttConnection] - No connection to broker: mosquitto
2018-05-29 23:19:26.834 [DEBUG] [org.openhab.binding.mysensors       ] - ServiceEvent REGISTERED - {org.eclipse.smarthome.config.discovery.DiscoveryService}={service.id=280, service.bundleid=13, service.scope=singleton} - org.openhab.binding.mysensors
2018-05-29 23:19:26.925 [DEBUG] [.discovery.MySensorsDiscoveryService] - Starting MySensors discovery scan
2018-05-29 23:19:27.032 [INFO ] [ateway.MySensorsNetworkSanityChecker] - Network Sanity Checker thread stopped
2018-05-29 23:19:27.191 [DEBUG] [ensors.factory.MySensorsCacheFactory] - Writing on cache given_ids, content: [0,1,99,4,5]
2018-05-29 23:19:27.242 [DEBUG] [nsors.handler.MySensorsBridgeHandler] - Initialization of the MySensors bridge DONE!
2018-05-29 23:19:27.250 [ERROR] [rotocol.mqtt.MySensorsMqttConnection] - Failed connecting to bridge...next retry in 10 seconds (Retry No.:0)

I've gone through your steps, Mysensors MQTT gateway remain offline.
What I'm wondering (since the directory structure is different), what is the total content of file: mqtt-eventbus.cfg? Can you post?

Ideas?

A little off topic but I'm struggling with a same type of scenario. Didnt want to start a new topic if the answer is here.
The battery I figured out but I'm having problems with the item (contact) and getting it to my sitemap.
I have checked both files "Contact" in items and "Text" in sitemap (when I add this line the sitemap doesnt load).

I will post my code if necessary, but can you tell me if a map is always necessary for door contacts? I have other types of sensors working without problems. Should my arduino send only specific words or boolean to make it work?

Just a quick idea: are you powering the RFM69 from the Rpi?
I use a Rpi Zero W and when I powered my radio NRF24 from that it doesnt get enough juice even with caps.
I now use a bigger USB-wall wart and use AMS1117-3.3 to power the radio (PA-version) and added caps.

My two cents

@mbj I think I finally solved the GW problem (signing password too short!).
Now I'm starting to deal with OH2. I'm seeing this in the log:

2018-04-03 00:10:59.717 [DEBUG] [rotocol.mqtt.MySensorsMqttConnection] - MQTT message received. Topic: mysensors-out/99/0/1/0/1, Message: 15.0
2018-04-03 00:10:59.747 [DEBUG] [rotocol.mqtt.MySensorsMqttConnection] - Message topic part: 99/0/1/0/1
2018-04-03 00:10:59.758 [DEBUG] [rotocol.mqtt.MySensorsMqttConnection] - Converted MQTT message to MySensors Serial format. Sending on to bridge: 99;0;1;0;1;15.0
2018-04-03 00:10:59.768 [DEBUG] [rsAbstractConnection$MySensorsReader] - Message from gateway received: 99;0;1;0;1;15.0
2018-04-03 00:10:59.777 [DEBUG] [rs.internal.gateway.MySensorsGateway] - Node 99 found in gateway
2018-04-03 00:10:59.785 [DEBUG] [rs.internal.gateway.MySensorsGateway] - Child 0 not present in node 99

I have one node sending temp & hum data (DHT11: child 0 hum, child 1 temp). OH2 wont autodiscover. Does this mean it must be added manually?
I hope there's an autodiscover if I'm going to build a network....

@mfalkvidd Made the password 10 characters. From looks of the logs, it's working now.
I cant believe I skipped the step of making the password longer... Just got too fixated on the password I came up with.

@anticimex I've built a new node, DHT11 that sends temp&hum data. I reconfigured Rpi with this:

sudo ./configure --my-transport=nrf24 --my-rf24-irq-pin=15 --my-signing-debug --my-signing=password --my-signing-password=XXXXXX --my-gateway=mqtt --my-controller-ip-address=127.0.0.1 --my-mqtt-user=YYYY --my-mqtt-password=ZZZZZ --my-mqtt-publish-topic-prefix=mysensors-out --my-mqtt-subscribe-topic-prefix=mysensors-in --my-mqtt-client-id=mygateway1 --my-leds-err-pin=12 --my-leds-rx-pin=16 --my-leds-tx-pin=18

This is what I get in gw syslog:

Apr  2 22:53:11 DietPi mysgw: Starting gateway...
Apr  2 22:53:11 DietPi mysgw: Protocol version - 2.2.0
Apr  2 22:53:11 DietPi mysgw: MCO:BGN:INIT GW,CP=RNNGLSQX,VER=2.2.0
Apr  2 22:53:11 DietPi mysgw: !SGN:BND:PWD<8
Apr  2 22:53:11 DietPi mysgw: !SGN:INI:BND FAIL
Apr  2 22:53:11 DietPi mysgw: TSF:LRT:OK
Apr  2 22:53:11 DietPi mysgw: TSM:INIT
Apr  2 22:53:11 DietPi mysgw: TSF:WUR:MS=0
Apr  2 22:53:11 DietPi mysgw: TSM:INIT:TSP OK
Apr  2 22:53:11 DietPi mysgw: TSM:INIT:GW MODE
Apr  2 22:53:11 DietPi mysgw: TSM:READY:ID=0,PAR=0,DIS=0
Apr  2 22:53:11 DietPi mysgw: MCO:REG:NOT NEEDED
Apr  2 22:53:11 DietPi mysgw: MCO:BGN:STP
Apr  2 22:53:11 DietPi mysgw: MCO:BGN:INIT OK,TSP=1
Apr  2 22:53:11 DietPi mysgw: GWT:RMQ:MQTT RECONNECT
Apr  2 22:53:11 DietPi mysgw: connected to 127.0.0.1
Apr  2 22:53:11 DietPi mysgw: GWT:RMQ:MQTT CONNECTED
Apr  2 22:53:11 DietPi mysgw: GWT:TPS:TOPIC=mysensors-out/0/255/0/0/18,MSG SENT
Apr  2 22:53:23 DietPi mysgw: TSF:MSG:READ,99-99-255,s=255,c=3,t=7,pt=0,l=0,sg=0:
Apr  2 22:53:23 DietPi mysgw: TSF:MSG:BC
Apr  2 22:53:23 DietPi mysgw: TSF:MSG:FPAR REQ,ID=99
Apr  2 22:53:23 DietPi mysgw: TSF:PNG:SEND,TO=0
Apr  2 22:53:23 DietPi mysgw: TSF:CKU:OK
Apr  2 22:53:23 DietPi mysgw: TSF:MSG:GWL OK
Apr  2 22:53:23 DietPi mysgw: SGN:SKP:MSG CMD=3,TYPE=8
Apr  2 22:53:23 DietPi mysgw: TSF:MSG:SEND,0-0-99-99,s=255,c=3,t=8,pt=1,l=1,sg=0,ft=0,st=OK:0
Apr  2 22:53:25 DietPi mysgw: TSF:MSG:READ,99-99-0,s=255,c=3,t=24,pt=1,l=1,sg=0:1
Apr  2 22:53:25 DietPi mysgw: SGN:SKP:MSG CMD=3,TYPE=24
Apr  2 22:53:25 DietPi mysgw: TSF:MSG:PINGED,ID=99,HP=1
Apr  2 22:53:25 DietPi mysgw: SGN:SKP:MSG CMD=3,TYPE=25
Apr  2 22:53:25 DietPi mysgw: TSF:MSG:SEND,0-0-99-99,s=255,c=3,t=25,pt=1,l=1,sg=0,ft=0,st=OK:1
Apr  2 22:54:18 DietPi mysgw: TSF:MSG:READ,99-99-0,s=1,c=3,t=16,pt=0,l=0,sg=0:
Apr  2 22:54:18 DietPi mysgw: SGN:SKP:MSG CMD=3,TYPE=16
Apr  2 22:54:18 DietPi mysgw: !SGN:NCE:GEN
Apr  2 22:54:23 DietPi mysgw: TSF:MSG:READ,99-99-0,s=0,c=3,t=16,pt=0,l=0,sg=0:
Apr  2 22:54:23 DietPi mysgw: SGN:SKP:MSG CMD=3,TYPE=16
Apr  2 22:54:23 DietPi mysgw: !SGN:NCE:GEN

This is kicking my butt... I cant understand that last part about the nonce
I will add the code from the node as soon as possible.

@bgunnarb I thought this was 2.2: https://forum.mysensors.org/topic/8201/openhab-2-2-binding-mqtt-support

Are you using the older binding? I'm doing battle with signing at the moment, so that could be holding up the function of OH2 as well.