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.
Use : for loading classes in entry_points
Merge pull request #2 from FlaPer87/messaging

Pass the driver instance to the listener instead of config