Add multiple provider network extension

The following commit adds the ability to associate multiple
different provider networks on a single network.

Implements blueprint map-networks-to-multiple-provider-networks

Change-Id: I3c70fb2426899f728a401566debab7f66e7246bc

etc/policy.json

@@ -21,16 +21,19 @@
     "create_network": "",
     "get_network": "rule:admin_or_owner or rule:shared or rule:external",
     "get_network:router:external": "rule:regular_user",
+    "get_network:segments": "rule:admin_only",
     "get_network:provider:network_type": "rule:admin_only",
     "get_network:provider:physical_network": "rule:admin_only",
     "get_network:provider:segmentation_id": "rule:admin_only",
     "get_network:queue_id": "rule:admin_only",
     "create_network:shared": "rule:admin_only",
     "create_network:router:external": "rule:admin_only",
+    "create_network:segments": "rule:admin_only",
     "create_network:provider:network_type": "rule:admin_only",
     "create_network:provider:physical_network": "rule:admin_only",
     "create_network:provider:segmentation_id": "rule:admin_only",
     "update_network": "rule:admin_or_owner",
+    "update_network:segments": "rule:admin_only",
     "update_network:provider:network_type": "rule:admin_only",
     "update_network:provider:physical_network": "rule:admin_only",
     "update_network:provider:segmentation_id": "rule:admin_only",