The rpc_backend configuration option has been deprecated in
oslo.messaging. The default and notitification transport_url
option defines the messaging backend and communication
parameters. Inclusion on zmq/rabbit options caused duplicate
declaration following deprecation of rpc_backend in service
modules.
This patch:
* remove parameter from zmq options
* remove parameter from rabbitmq option
* update spec test
Change-Id: Ia981f1a847a428e0f07656d0922e195982e4e2f9