Abstract container commands

[ribalba]

Currently in the runner we call all the docker commands by executing a new process. While this is secure in the way that the docker command api stays the same it is not ideal. I would want to introduce a container abstraction layer. So we can
a) use https://docker-py.readthedocs.io/en/stable/index.html to manage our containers if we choose too. I would like to see how much overhead the spawing of the new processes adds
b) add Podman (bigger refactor)

nothing too important right now but should not be lost.