MidoNet valid_service addition

MidoNet needs its low-level API to have access to the admin token.
Thus, it needs to be considered a valid service. This patch adds it
to the list of valid services so that the identity-service relation
can be completed successfully and with the admin_token.

hooks/keystone_utils.py

@@ -255,6 +255,10 @@ valid_services = {
     "image-stream": {
         "type": "product-streams",
         "desc": "Ubuntu Product Streams"
+    },
+    "midonet": {
+        "type": "network-overlay",
+        "desc": "MidoNet low-level API"
     }
 }