conf: Deprecate 'masakari_topic' RPC options

Giving provision to operators to configure RPC topic for
masakari-engine service can lead to some errors pointed by the
bug: 1643834. So there is no need to let operators choose the RPC
topic for engine service. It's best to deprecate and remove this
option as it's really easy to break masakari by using this option,
and there is little gain for deployers in changing this option.

Change-Id: Ie8e55762201cbf69f90838217098860ded51a307

masakari/conf/engine.py

@@ -19,6 +19,12 @@ from oslo_config import cfg
 rpcapi_opts = [
     cfg.StrOpt("masakari_topic",
             default="ha_engine",
+            deprecated_for_removal=True,
+            deprecated_since='3.0.0',
+            deprecated_reason="""
+Configurable RPC topic provides little value and it can easily break
+Masakari if operator configures it to the same topic used by other OpenStack
+services.""",
             help="""
 This is the message queue topic that the masakari engine 'listens' on. It is
 used when the masakari engine is started up to configure the queue, and

releasenotes/notes/deprecate-topic-opt-af83f82143143c61.yaml

@@ -0,0 +1,5 @@
+---
+deprecations:
+  - |
+    The ``masakari_topic`` config option is now deprecated and will be removed
+    in the Queens release.