Deprecate rpc_backend option

Option "rpc_backend" from group "DEFAULT" is deprecated for removal
(Replaced by [DEFAULT]/transport_url). Its value may be silently
ignored in the future.

Change-Id: I6ff5a9e734d5ba3de12a43e6f57d5a3ce214db5e
Implements: blueprint deprecate-rpc-backend

defaults/main.yml

@@ -54,7 +54,6 @@ sahara_system_user_home: "/var/lib/{{ sahara_system_user_name }}"
 sahara_engine_host: "{{ internal_lb_vip_address }}"
 
 ## RabbitMQ info
-sahara_rpc_backend: sahara.openstack.common.rpc.impl_kombu
 sahara_rabbitmq_userid: sahara
 sahara_rabbitmq_vhost: /sahara
 sahara_rabbitmq_use_ssl: False

releasenotes/notes/remove_rpc_backend-89135235e3513394.yaml

@@ -0,0 +1,5 @@
+---
+deprecations:
+  - |
+    Remove ``sahara_rpc_backend`` option due to deprecation of
+    rpc_backend option in oslo.messaging.

templates/sahara.conf.j2

@@ -25,7 +25,6 @@ proxy_user_role_names = {{ sahara_proxy_user_role_names }}
 {% endif %}
 
 ## RPC Backend
-rpc_backend = {{ sahara_rpc_backend }}
 transport_url = rabbit://{% for host in sahara_rabbitmq_servers.split(',') %}{{ sahara_rabbitmq_userid }}:{{ sahara_rabbitmq_password }}@{{ host }}:{{ sahara_rabbitmq_port }}{% if not loop.last %},{% else %}/{{ sahara_rabbitmq_vhost }}{% endif %}{% endfor %}