Merge ~wesley-wiedenmeier/cloud-init:integration-testing-mro into cloud-init:master

[Wesley Wiedenmeier]

Integration Testing: improve testcase subclassing

Use inspect.getmro(mod) rather than mod.__bases__ to test if a potential
testcase class inherits from CloudTestCase. This allows testcases to be based on CloudTestCase indirectly, adding greater flexibility to the structure of test classes.

diff --git a/tests/cloud_tests/testcases/__init__.py b/tests/cloud_tests/testcases/__init__.py
index 182c090..a1d86d4 100644
--- a/tests/cloud_tests/testcases/__init__.py
+++ b/tests/cloud_tests/testcases/__init__.py
@@ -21,7 +21,7 @@ def discover_tests(test_name):
         raise ValueError('no test verifier found at: {}'.format(testmod_name))
 
     return [mod for name, mod in inspect.getmembers(testmod)
-            if inspect.isclass(mod) and base_test in mod.__bases__ and
+            if inspect.isclass(mod) and base_test in inspect.getmro(mod) and
             getattr(mod, '__test__', True)]