I used this container to connect my ownTracks devices to a common MQTT broker.
Dockerfile can be found here: https://github.com/maxheadroom/Mosquitto
To run it, just do this:
docker start -name owntracks maxheadroom/owntracks
for debugging purposes you can subscribe to the MQTT broker with command line tools:
docker exec -ti owntracks /usr/local/bin/mosquitto_sub -t "owntracks/#"