Replace tearDown with addCleanup - Part 2

Replace tearDown with addCleanup in some cinder unit tests.

Infra team has indicated that tearDown should not be used and should
be replaced with addCleanup in all places.

Remove duplicated self.stubs and self._mox declaration in
cinder/tests/test_windows.py.

Implements blueprint replace-teardown-with-addcleanup

Change-Id: I5865cf0197e1d8229afc706b9b14b746f09b5acd
Merge "Replace tearDown with addCleanup - Part 2"