Configurable Notifications Routing

Openstack projects produce a wide variety of notification messages describing events occurring inside the system. These may be used for usage billing, performance monitoring, and other integration tasks. This blueprint proposes an optional notification driver that can route notification events to other notification drivers based on the notification's event_type, using a configuration specified in a json config file. This will allow some events to be delivered via a more robust delivery mechanism like AMQP that has guaranteed delivery, while others are delivered via lighter weight methods that are faster and have a higher throughput, but may not have such guarantees (which may not be needed for the application they are being used for), and still other notifications, not needed for a given install, may be dropped altogether.