Add support for tests defining resource_cleanup

Add support for tests having a resource_cleanup method. Whether this
is run or not is dictated by the class variable
'run_resource_cleanup'. By default this will be True but any test
can switch it to False so that resources created by the tests are
preserved. Helpful for debugging failures.

FWIW future work might include automatically disabling resource
cleanup if a test fail is detected.

zaza/openstack/charm_tests/test_utils.py

@@ -93,6 +93,24 @@ def audit_assertions(action,
 class OpenStackBaseTest(unittest.TestCase):
     """Generic helpers for testing OpenStack API charms."""
 
+    @classmethod
+    def resource_cleanup(cls):
+        """Cleanup any resources created during the test run.
+
+        Override this method with a method which removes any resources
+        which were created during the test run. If the test sets
+        "self.run_resource_cleanup = False" then cleanup will be
+        skipped.
+        """
+        pass
+
+    @classmethod
+    def tearDown(cls):
+        """Run teardown for test class."""
+        if cls.run_resource_cleanup:
+            logging.info('Running resource cleanup')
+            cls.resource_cleanup()
+
     @classmethod
     def setUpClass(cls, application_name=None):
         """Run setup for test class to create common resourcea."""
@@ -106,6 +124,7 @@ class OpenStackBaseTest(unittest.TestCase):
         cls.lead_unit = model.get_lead_unit_name(
             cls.application_name,
             model_name=cls.model_name)
+        cls.run_resource_cleanup = True
         logging.debug('Leader unit is {}'.format(cls.lead_unit))
 
     @contextlib.contextmanager