Removes stubs from unit tests

self.stubs in TestCase and BaseTestCase classes use moxstubout
module which uses mox. OpenStack is moving to python 3 which
will not support mox. This patch removes the use of self.stubs
for all the unit test cases.

Change-Id: I0e5aa50edcbb1913c5143bb93efea965f5d5ebfb