[FLOC-965] Acceptance testing against racksapce.

This is based on #1010. The relative diff is [here](https://github.com/ClusterHQ/flocker/compare/acceptance-runner-FLOC-1070...rackspace-acceptance-FLOC-965).

The linking tests fail due to [FLOC-1084](https://clusterhq.atlassian.net/browse/FLOC-1084).


It turns out the blocks exactly matched the blocks in the documentation. I've done some work to limit the amount of code that cares about fabric, and started to use `flocker.common._ipc` [here](https://github.com/ClusterHQ/flocker/compare/rackspace-acceptance-FLOC-965...get-rid-of-fabric). But rackspace tends to reuse IP addresses, so I started getting ``WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!`` when running the tests.