Use module imports
No need to alias nova.tests.utils
Document why _get_running_instance is overridden
Set class-level driver init values
Fix instantiation of a fake DockerDriver

* Move mock client to nova.tests.virt.docker.mock_client
* Allow overriding of the client class in DockerDriver.__init__
* Mock out the one DockerDriver method that depended on 'fake'
* Remove DockerDriver.fake attribute
Merge pull request #10 from bcwaldon/fix-tests

Correct fake client/driver initialization & small nit-picky fixes