With YP LTS initiative, we may get into a time when the AutoBuilder itself can no longer support an older release (e.g. the automated testing infrastructure has changed, etc.).

It might also increase usage of the AutoBuilder if it was easier to setup/try.

This container would be a blend of the poky-container [1,2] and the buildbot-worker [3,4] container. The autobuilder-master container might be able to be simpler, but this worker container will need all the bits to build and run tests. Testing may benefit from running QEMU outside the container using libvirt or other means.

Although it would be tempting to run Docker-in-Docker, this is ill advised [5] and instead the docker socket should be bind mounted:
'docker run -v /var/run/docker.sock:/var/run/docker.sock ...'

Similarly, the persistent build directories should be bind mounted docker volumes (local driver). 

[1] https://github.com/crops/poky-container
[2] https://hub.docker.com/r/crops/poky
[3] https://github.com/buildbot/buildbot/blob/master/worker/Dockerfile.py3
[4] https://hub.docker.com/r/buildbot/buildbot-worker
[5] https://jpetazzo.github.io/2015/09/03/do-not-use-docker-in-docker-for-ci/