Pass the driver instance to the listener instead of config

There are a couple of cases where having the driver instance is a good
thing for the Listener, though, I would like to use the connection
management as motivation here:

Instead of creating a new connection for every Listener it would be
possible to let the driver instance managing the whole connect /
reconnect and session handling process.

In the old implementation, when a reconnect happens, the connection
instance calls every consumer and sets the new connection / session to
them.

See: http://github.com/openstack/oslo-incubator/blob/master/openstack/common/rpc/impl_qpid.py#L368

Listeners can access the config instance through the driver instance.

openstack/common/messaging/drivers/base.py

@@ -20,8 +20,8 @@ class Listener(object):
 
     __metaclass__ = abc.ABCMeta
 
-    def __init__(self, conf, target):
-        self.conf = conf
+    def __init__(self, driver, target):
+        self.driver = driver
         self.target = target
 
     @abc.abstractmethod