Sync latest notifier changes from openstack-common

Sync latest notifier changes from openstack-common

Updates Quantum with the latest changes from openstack-commons
notifier package:

    Rename rabbit_notifier to rpc_notifier.

    The previous rabbit_notifier module is generic and can be used
    for all RPC notifications.

    This commit moves the rabbit_notifier module to rpc_notifier and
    adds a new deprecated rabbit_notifier module which can be used for
    Grizzly so that users can have a chance to easily upgrade this
    config setting.

Also updates the agent code and config file to reflect this change
(and get unit tests to pass)

Fixes LP Bug #1075330.

Change-Id: If9a4f5fa27638b25a29b66dbfed757554358ff7c