docker: update to docker-py 0.3.0, plus full port binding support etc. from #5639

This rebases the changes against #5639 from the current devel branch, plus adds (well, requires) support for `docker-py` 0.3.0, which is the latest version. (See discussion from `ansible-devel` list here: https://groups.google.com/forum/#!topic/ansible-devel/L57eChJ93Tk)