Sketch of how this will work and what the tests will look like.
Got tests working with LocalVolumeManager.
Implement tests and RemoteVolumeManager.
Switch VolumeService to use the higher-level IPC interface.
Make flake8 happy.
Add interface implementation.
Clarify docstring.
Another docstring clarification.
Address review comment: Better docstring.
Address review comment: Remove incorrect reference to SSH.
Address review comment: Correct docstring style.
Merge pull request #242 from ClusterHQ/high-level-ipc-238

Higher level IPC abstraction.

Fixes #238.