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: I6c7aa04a3a3aaaab7f428cb86549a4d043af802f

openstack-dev/pbr,openstack-dev/pbr,openstack-dev/pbr