Add metering extension and base class

This a part of the blueprint bandwidth-router-label

This patch initiates the blueprint by adding base class
to associate labels and metering rules to tenant's routers.

Change-Id: Ia93b49d881e79c3291730cff7b80f26c56fedb48

etc/policy.json

@@ -114,5 +114,13 @@
     "get_network_profile": "",
     "update_policy_profiles": "rule:admin_only",
     "get_policy_profiles": "",
-    "get_policy_profile": ""
+    "get_policy_profile": "",
+
+    "create_metering_label": "rule:admin_only",
+    "delete_metering_label": "rule:admin_only",
+    "get_metering_label": "rule:admin_only",
+
+    "create_metering_label_rule": "rule:admin_only",
+    "delete_metering_label_rule": "rule:admin_only",
+    "get_metering_label_rule": "rule:admin_only"
 }