Change assertTrue(isinstance()) by optimal assert
Change assertTrue(isinstance()) by optimal assert

Some of tests use different method of
assertTrue(isinstance(A, B)) or assertEqual(type(A), B).
The correct way is to use assertIsInstance(A, B) provided
by testtools

Change-Id: I067266b9969dd5f9aefe0bdb3f8a8e5c6d488fdf

coreycb/charms.openstack,ajkavanagh/charms.openstack