Parameterize value `enabled` for cloudwatch-api

Reason: Heat CloudWatch API has been removed from
openstack Queens and above.
Stacklight team have fired Alert about heat cloudwatch but
its a false positive since in recent heat this cloudwatch
is not longer present.

Change-Id: Id540c386f87279d4601b13510b4a548e0f20721f
Related-Prod: PROD-25742 (PROD:25742)
(cherry picked from commit 50676628308afb545d180b5c237b9e9540a0ea85)
diff --git a/apache/server/proxy/openstack/heat.yml b/apache/server/proxy/openstack/heat.yml
index d8f222a..86f9d54 100644
--- a/apache/server/proxy/openstack/heat.yml
+++ b/apache/server/proxy/openstack/heat.yml
@@ -40,7 +40,7 @@
             address: ${_param:apache_proxy_openstack_api_address}
           ssl: ${_param:apache_proxy_ssl}
         apache_proxy_openstack_api_heat_cloudwatch:
-          enabled: true
+          enabled: ${_param:openstack_heat_cloudwatch_api_enabled}
           type: proxy
           name: openstack_api_heat_cloudwatch
           check: false