Add more association support to network API

Adds API support to:
- Disassociate only host from network
- Disassociate only project from network
- Associate network with host (project already supported)

New functionality is added to a new extension networks_associate,
but the original networks extension is modified to allow networks_associate
to extend how it needs to. The original behavior of the networks extension is
preserved (no new functionality, nor change in existing behavior) in
terms of the API presented.

Bumps RPC API version for network RPC server version in order add
the associate function which allows to both associate and disassociate
a network with a host and or tenant. Has overlap with disassociate
and add_network_to_project but these are kept for backwards compatibility

DocImpact
Implmenents: blueprint apis-for-nova-manage
Change-Id: I78fd76e0696d1c872646355ab04d32f051551def

doc/api_samples/all_extensions/extensions-get-resp.json

@@ -296,6 +296,14 @@
             "namespace": "http://docs.openstack.org/compute/ext/networks/api/v1.1",
             "updated": "2011-12-23T00:00:00+00:00"
         },
+        {
+            "alias": "os-networks-associate",
+            "description": "Network association support",
+            "links": [],
+            "name": "NetworkAssociationSupport",
+            "namespace": "http://docs.openstack.org/compute/ext/networks_associate/api/v2",
+            "updated": "2012-11-19T00:00:00+00:00"
+        },
         {
             "alias": "os-quota-class-sets",
             "description": "Quota classes management support",

doc/api_samples/all_extensions/extensions-get-resp.xml

@@ -125,6 +125,9 @@
   <extension alias="os-networks" updated="2011-12-23T00:00:00+00:00" namespace="http://docs.openstack.org/compute/ext/networks/api/v1.1" name="Networks">
     <description>Admin-only Network Management Extension</description>
   </extension>
+  <extension alias="os-networks-associate" updated="2012-11-19T00:00:00+00:00" namespace="http://docs.openstack.org/compute/ext/networks_associate/api/v2" name="NetworkAssociationSupport">
+    <description>Network association support</description>
+  </extension>
   <extension alias="os-quota-class-sets" updated="2012-03-12T00:00:00+00:00" namespace="http://docs.openstack.org/compute/ext/quota-classes-sets/api/v1.1" name="QuotaClasses">
     <description>Quota classes management support</description>
   </extension>