Skip alarm tests when Aodh is not available

This change makes sure the scenario tests depending on Aodh alarm are
not executed when Aodh is not available.

With this change tests are skipped if one of the conditions below is
met.

- telemetry-tempest-plugin is installed and [service_available] aodh is
  set to False

- alarming service type is not found in keystone catalog

Change-Id: I380223ad26692ff9967dcb070a7b7b73e5746401

heat_tempest_plugin/tests/scenario/test_aodh_alarm.py

@@ -21,6 +21,8 @@ from heat_tempest_plugin.tests.scenario import scenario_base
 LOG = logging.getLogger(__name__)
 
 
+@test.requires_service_type('alarming')
+@test.requires_service('aodh')
 class AodhAlarmTest(scenario_base.ScenarioTestsBase):
     """Class is responsible for testing of aodh usage."""
     def setUp(self):