Change assertTrue(isinstance()) by optimal assert

assertTrue(isinstance(A, B)) or assertEqual(type(A), B) in tests
should be replaced by assertIsInstance(A, B) provided by testtools.

I have searched all the tests, there is only one wrong usage.

Change-Id: Ib1db1a2dca7b5d8cbfe823973e4b571d0f0925c5
Closes-bug: #1268480
Merge "Change assertTrue(isinstance()) by optimal assert"