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: I5e7afcdc7be36e64168ef850749dfcb5a19e784a
Closes-Bug: #1268480
Merge "Change assertTrue(isinstance()) by optimal assert"