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: Ia8d38f73c159c7ef943a8f6cfe72b945cc493947
Closes-bug: #1268480
Merge "Change assertTrue(isinstance()) by optimal assert"