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: I8426ee1f6387602660f2d768883d18ab2f04c6f0
Closes-bug: #1268480
Merge "Change assertTrue(isinstance()) by optimal assert"