Allow floating IP pools to be deleted

Fixes bug #1022237

If you delete all the floating IPs associated with a floating IP, the
pool still shows up in os-floating-ip-pools extension.

Fix this by using model_query() in the DB layer so that we ignore
deleted floating IPs.

Change-Id: I30d2e716e931400ca4b798b51bb26a73a7747808

nova/db/sqlalchemy/api.py

@@ -720,7 +720,7 @@ def floating_ip_get(context, id):
 def floating_ip_get_pools(context):
     session = get_session()
     pools = []
-    for result in session.query(models.FloatingIp.pool).distinct():
+    for result in model_query(context, models.FloatingIp.pool).distinct():
         pools.append({'name': result[0]})
     return pools