Clean up started volume services in tests.

The test_preattach_status_volume test was failing due to state left by
another test. The interim solution was to skip the aforementioned test.
I tracked down the problem to 4 tests in test_admin_actions.py that
call self.start_service('volume', host='test'), and don't stop the
service. Stopping it in all 4 tests solves the problem.

HOWEVER, I don't know why these started services caused this particular
test to fail. I am still working to figure that out, but maybe someone
has an idea.

Change-Id: I2a5caaae9f61e7c7617c934917a10cf1cf3c0db6
Fixes: bug 1153108
Merge "Clean up started volume services in tests."