Replace notifier with oslo.messaging

Oslo messaging works slightly differently in that you create a Notifier
object once which contains config such as publisher_id and then you
re-use that object when issuing messages.

DocImpact: The options for setting up RPC and notifications have changed
to reflect oslo.messaging.

Blueprint: oslo-messaging
Change-Id: I2d08fb405e68df37866b3799ab7339ebd9894f05
Merge "Replace notifier with oslo.messaging"