Remove use of oslo.messaging rpc_backend

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

manifests/messaging/rabbit.pp

@@ -237,7 +237,6 @@ rabbit_password, rabbit_virtual_host parameters have been deprecated by the \
                       'oslo_messaging_rabbit/ssl_cert_file' => { value => $kombu_ssl_certfile },
                       'oslo_messaging_rabbit/ssl_key_file' => { value => $kombu_ssl_keyfile },
                       'oslo_messaging_rabbit/ssl_version' => { value => $kombu_ssl_version },
-                      'DEFAULT/rpc_backend' => { value => 'rabbit' },
                     }
 
   create_resources($name, $rabbit_options)

manifests/messaging/zmq.pp

@@ -112,7 +112,6 @@ define oslo::messaging::zmq(
     'DEFAULT/rpc_zmq_topic_backlog' => { value => $rpc_zmq_topic_backlog },
     'DEFAULT/use_pub_sub' => { value => $use_pub_sub },
     'DEFAULT/zmq_target_expire' => { value => $zmq_target_expire },
-    'DEFAULT/rpc_backend' => { value => 'zmq' },
   }
 
   create_resources($name, $zmq_options)

spec/defines/oslo_messaging_rabbit_spec.rb

@@ -29,7 +29,6 @@ describe 'oslo::messaging::rabbit' do
        is_expected.to contain_keystone_config('oslo_messaging_rabbit/rabbit_transient_queues_ttl').with_value('<SERVICE DEFAULT>')
        is_expected.to contain_keystone_config('oslo_messaging_rabbit/heartbeat_timeout_threshold').with_value('<SERVICE DEFAULT>')
        is_expected.to contain_keystone_config('oslo_messaging_rabbit/heartbeat_rate').with_value('<SERVICE DEFAULT>')
-       is_expected.to contain_keystone_config('DEFAULT/rpc_backend').with_value('rabbit')
       end
     end