Add docker-py integration tests aginst the docker daemon

This clones and run the integration tests for docker-py master as part
of the integration tests created on master.  docker-py hits the api
directly and should be a good way to identify regressions in the api.

The tests will be pinning to a specific tag and updated when a new version of docker-py is released so that we track releases and not master to ensure API compatibility.

 
Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Yeah, I think it'd be better.  Probably in some way that makes it optional, like `project/make/.ensure-busybox` does.  I can take over if you'd rather -- I know Bash isn't your favorite. :smile: :heart: