Generate Tempest service list rather than hard-code it

The list of services that Tempest used to set its 'service_available'
config values was hard-coded. To be plugin-friendly have each
service (project) add its name to the TEMPEST_SERVICES variable
and use that for setting the 'service_avilable' values.

Change-Id: I208efd7fd0798b18ac2e6353ee70b773e84a2683
diff --git a/lib/cinder b/lib/cinder
index d76a41d..9f70b2a 100644
--- a/lib/cinder
+++ b/lib/cinder
@@ -79,6 +79,9 @@
 
 VOLUME_NAME_PREFIX=${VOLUME_NAME_PREFIX:-volume-}
 
+# Tell Tempest this project is present
+TEMPEST_SERVICES+=,cinder
+
 
 # Functions
 # ---------