Functional tests for volume removal from docker.
Implement removal.
Address review comment: Stop the service as part of test cleanup.
Address review comment: Better assertion.
Address review comment: Return result of None.
Fix bad callback.
Less stupid assertion.
Merge remote-tracking branch 'refs/remotes/origin/master' into unexpose-volume-161
Merge pull request #164 from ClusterHQ/unexpose-volume-161

Unexpose volumes from docker.

Fixes #161.