Older Docker Server versions

[lstephen]

By default, the latest possible version of docker-py will be installed by pip. But, the latest versions of docker-py will default to a higher version of the Docker API.

This can result in error messages such as: client is newer than server (client API version: 1.30, server API version: 1.24).

Perhaps we should force construi onto the oldest possible version of docker-py. In theory this provides the widest range of compatibility with Docker versions without having to specify an explicit version.

It should also be possible to set the API version when creating the Docker client https://github.com/docker/docker-py/blob/2.1.0/docker/constants.py#L5

[lstephen]

Better than using minimum, is using auto, https://github.com/docker/docker-py/blob/master/docker/api/client.py#L77

We don't need to use an older version of docker-py in this case either.