Is the MQTT Broker on the same host (the rPi2) ?
If yes, use: mymosquitto.url=tcp://localhost:1883
Do the following:
- Enable debug in the openHAB console:
log:set DEBUG org.openhab.binding.mqtt
&log:set DEBUG org.openhab.io.transport.mqtt
- Uninstall from PaperUI the MQTT Action add-on (if installed)
- Shut down OH2
- Delete file
/var/lib/openhab2/config/org/openhab/mqtt.config
and - Start OH2
Also, make sure that the clientId (openhab2) is not used by any other client
Which release of OH2 are you using?