[IMPROV] Redirect testcase.assertRegexpMatches

With Python 3 the assertRegexpMatches was renamed to assertRegex, but
the old name is still available (with a deprecation warning). To remove
it, aspects.TestCase adds a assertRegex in Python 2 which calls the
actual method. All usages have been replaced.

Change-Id: I988ce51bf72293d93069ee3f1bfaac786febeb94
Merge "[IMPROV] Redirect testcase.assertRegexpMatches"