Make the checks of identity status code strict

Some identity API tests check response status codes like:

 self.assertTrue(resp['status'].startswith('2'))

This way cannot detect the status code changes and that means
Tempest cannot block the backward incompatibility changes for
Keystone.

This patch makes these checks strict by specifying particular
status codes.

Closes-Bug: #1293982

Change-Id: Icab5ff57aaa06e313da209f87ced4c2135ab5343
orchestration API base class rename clear* functions

Rename the clear* functions as they are "private" and only called
in tearDownClass - being effictively garbage collectors for the test
class we want to make clear that these should not be called from
the tests themselves.

Change-Id: I8b022a730af981ca202fe9f190d91ef9af3bf92d
Merge "Make the checks of identity status code strict"