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/marconi b/lib/marconi
index 6b9ffdc..1eaebbd 100644
--- a/lib/marconi
+++ b/lib/marconi
@@ -51,6 +51,10 @@
 MARCONICLIENT_REPO=${MARCONICLIENT_REPO:-${GIT_BASE}/openstack/python-marconiclient.git}
 MARCONICLIENT_BRANCH=${MARCONICLIENT_BRANCH:-master}
 
+# Tell Tempest this project is present
+TEMPEST_SERVICES+=,marconi
+
+
 # Functions
 # ---------