Add support for the cloudkitty service

CloudKitty (Rating-as-a-Service for OpenStack) requires the creation of a
service in keystone to properly work. This patch registers cloukitty as a valid
service to enable the relation between those two charms.

hooks/keystone_utils.py

@@ -269,6 +269,10 @@ valid_services = {
     "midonet": {
         "type": "network-overlay",
         "desc": "MidoNet low-level API"
+    },
+    "cloudkitty": {
+        "type": "rating",
+        "desc": "CloudKitty Rating API"
     }
 }