Introduce support for oslo.messaging amqp driver configuration

Introduce support for oslo.messaging amqp driver configuration

This commit adds support for the oslo.messaging amqp rpc_backend which enables
the AMQP 1.0 driver. A proposed feature for the Newton oslo.messaging release is an
update to the AMQP 1.0 driver to support a stateless messaging interconnect for
RPC traffic[1].

This patch:
* use oslo::messaging::amqp resource
* add new parameters for the oslo_messaging_amqp driver
* update spec tests for amqp as alternate rpc_backend
* add feature release note

[1] https://blueprints.launchpad.net/oslo.messaging/+spec/amqp-dispatch-router

Change-Id: I2095cee083c9ca2390df703ad6e3216e428989f9