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: Ia94ff8a08d298e5e90bfdefca00a9ff0efa31053

openstack/monasca-log-api,stackforge/monasca-log-api,stackforge/monasca-log-api,stackforge/monasca-log-api,openstack/monasca-log-api,openstack/monasca-log-api