Add control_exchange option to common/config.py

fixes bug 1062517

Follows the instructions in the openstack/common/rpc/__init__.py and
defines a control_exchange option.

Change-Id: I92c50e1aea44954b2c9d62db1df536b9044b6951

quantum/common/config.py

@@ -50,7 +50,11 @@
     cfg.IntOpt('max_subnet_host_routes', default=20),
     cfg.StrOpt('state_path', default='.'),
     cfg.IntOpt('dhcp_lease_duration', default=120),
-    cfg.BoolOpt('allow_overlapping_ips', default=False)
+    cfg.BoolOpt('allow_overlapping_ips', default=False),
+    cfg.StrOpt('control_exchange',
+               default='quantum',
+               help='AMQP exchange to connect to if using RabbitMQ or Qpid')
+
 ]
 
 # Register the configuration options