Separate prometheus related tests

We have an issue, that tempest doesn't distinguish between
branches. New features aren't available on old branches and
so we can't execute testing, which involves sg-core or prometheus
on old branches. Separating sg-core and prometheus related tests
allows us to use tempest regex to execute those tests only on
branches, which have the required features.

This also fills in service_available requirements, to make it
clear which tests are runable on prometheus based storage
and which are runable on gnocchi based storage.

Change-Id: Ic5bea08295d8c85303c676706415e093625ee16f
diff --git a/telemetry_tempest_plugin/aodh/api/base.py b/telemetry_tempest_plugin/aodh/api/base.py
index 816f204..7298170 100644
--- a/telemetry_tempest_plugin/aodh/api/base.py
+++ b/telemetry_tempest_plugin/aodh/api/base.py
@@ -31,6 +31,8 @@
         super(BaseAlarmingTest, cls).skip_checks()
         if not CONF.service_available.aodh:
             raise cls.skipException("Aodh support is required")
+        if not CONF.service_available.gnocchi:
+            raise cls.skipException("Gnocchi support is required")
 
     @classmethod
     def setup_clients(cls):