Add a Docker Latent BuildSlave implementation

This is inspired from https://github.com/elbaschid/dockbot/blob/make_single_command_executable/dockbot/slaves/dockerslave.py.

Apart from the concept few parts are remaining though.

A container remains a container, I just mean that docker itself and the master process are more tightly coupled ... I tend to virtualize everything, hence this is not my favorite setup, but if you have a better sentence to describe that, be my guest !