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: I9053c9deaa71ee12e10db73b19250b3a32f3d93c
Closes-bug: #1268480
1 file changed
tree: 930ff8231a133bbe31d4cd79763292a83b82e983
  1. manila_tempest_tests/