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/ironic b/lib/ironic
index afbc3e0..b8838f5 100644
--- a/lib/ironic
+++ b/lib/ironic
@@ -42,6 +42,9 @@
 IRONIC_SERVICE_PROTOCOL=http
 IRONIC_HOSTPORT=${IRONIC_HOSTPORT:-$SERVICE_HOST:6385}
 
+# Tell Tempest this project is present
+TEMPEST_SERVICES+=,ironic
+
 
 # Functions
 # ---------