Switch to official docker-py-0.3.2 and six

This is the PR I was going to send to get back onto the official docker-py. You need to upgrade to 0.3.2 anyway before the TTY size issue can be fixed cleanly, so these changes are needed.

Somebody who knows why docker-py was being vendored before will need to pick this up and vendor 0.3.2 with the necessary patches, if you're certain that is still needed.

[off-topic]
Using looser requirements (i.e. 'docker-py>=version') would maybe alleviate some of the 'conflict' issues with using non-vendored projects from PyPi.
[/off-topic]