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: I4a5413f9d90d2e581044885a440a46bf3d76598f
Closes-Bug: #1268480
Merge "Change assertTrue(isinstance()) by optimal assert"