Acceptance tests

Fixes #315.
The benefits of having these live inside flocker outweigh the downsides that I can think of. I propose skipping the tests if the nodes to run them on are not available (as is the case on Buildbot) and telling coverage to ignore this module.

Keeping the tests with the code means that they can use existing test infrastructure (e.g. our NamespacedDockerClient) without code duplication and sync issues.