Deprecate unused [DEFAULT] http_timeout

This parameter has never been used by any logic since Aodh was splitted
out from Ceilometer.

Change-Id: I667ed60cbf751b1668b86bf7be0b946fe6d84f60

aodh/service.py

@@ -36,6 +36,9 @@ profiler_opts = importutils.try_import('osprofiler.opts')
 OPTS = [
     cfg.IntOpt('http_timeout',
                default=600,
+               deprecated_for_removal=True,
+               deprecated_reason=('This parameter is not used now and has no '
+                                  'effect.'),
                help='Timeout seconds for HTTP requests. Set it to None to '
                     'disable timeout.'),
     cfg.IntOpt('evaluation_interval',

releasenotes/notes/deprecate-unused-http_timeout-74fd60a4c26afd88.yaml

@@ -0,0 +1,5 @@
+---
+deprecations:
+  - |
+    The ``[DEFAULT] http_timeout`` parameter has been deprecated. This
+    parameter has been unused thus has had no effect.