Fix test runs with no charm_name

Fix z-o-t so that tests that specify an application name can
be run irrespective of whether the charm_name has been set in
tests.yaml. Closes issue openstack-charmers#442

zaza/openstack/charm_tests/test_utils.py

@@ -127,11 +127,11 @@ def setUpClass(cls, application_name=None, model_alias=None):
         else:
             cls.model_name = model.get_juju_model()
         cls.test_config = lifecycle_utils.get_charm_config(fatal=False)
-        charm_under_test_name = cls.test_config['charm_name']
 
         if application_name:
             cls.application_name = application_name
         else:
+            charm_under_test_name = cls.test_config['charm_name']
             deployed_app_names = model.sync_deployed(model_name=cls.model_name)
             if charm_under_test_name in deployed_app_names:
                 # There is an application named like the charm under test.