If tests are not run in the default order nosetests runs them in it
is possible that the monkey patching of fake_libvirt utils is not
properly cleaned up. Use fixtures.MonkeyPatch to monkey patch
fake_libvirt_utils in test setUp ensuring the monkey patching is
reverted properly after each test.
Part of blueprint grizzly-testtools
Change-Id: Ie691cbc777c01fa8a5affa3271f36776ea9648b9