Separate backends by type

Adding telemetry_services config group.

Deprecating old gnocchi and sg-core service options.

Splitting the backend specific tests into their own paths so they
can be disabled based on configuration.

Change-Id: I4ca0e217998825589f755d1169aa0600cef14248
diff --git a/.zuul.yaml b/.zuul.yaml
index 613717d..de2a73b 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -53,6 +53,9 @@
           $TEMPEST_CONFIG:
             service_available:
               sg-core: True
+            telemetry_services:
+              aodh_gnocchi: True
+              aodh_prometheus: True
             telemetry:
               disable_ssl_certificate_validation: True
       tempest_test_regex: telemetry_tempest_plugin