Use testtools as base test class.

Minor tests refactoring due to use testtools:
 - added missed setUp() and tearDown() to call these functions in
   base test case.
 - removed some superfluous tearDown() calls.
 - moved test_crud_inherited_role_grants_failed_if_disabled() method
   to separate class.

Fixes for python 2.6 enviroment:
 - replaced `with self.assertRaises(Exception): foo()` to
   `self.assertRaises(Exception, foo)
 - added to safe_repr(), assertDictEqual() and assertRaisesRegexp() methods
   to TestCase() class in keystone/test.py

Fixes bug 1179009

Change-Id: Iea67ad10d02db82fc8ed79b1096ddb5233925bfd
Merge "Use testtools as base test class."