Use assertIn and assertNotIn instead of assertTrue/assertFalse

The assertIn and assertNotIn is defined in testtools, it is expected to
work with all testtools supported python version.

The assertIn and assertNotIn is more verbose when a real issue occurs.

Change-Id: I7a21a6e38f606deb58b5bade6414f6c4a4142f4b
Merge "Use assertIn and assertNotIn instead of assertTrue/assertFalse"