Configure listener_pool_name for designate-sink service

Set listener_pool_name to designate-sink by default to
make sure notifications are delivered to all subscribers
with notifications topic (designate,ceilometer)

Change-Id: Iacc74ac33e828e2a52720235e6705c370477b791
Related-Prod: PROD-20427
diff --git a/metadata/service/server/single.yml b/metadata/service/server/single.yml
index 6fec47d..e3884c5 100644
--- a/metadata/service/server/single.yml
+++ b/metadata/service/server/single.yml
@@ -35,3 +35,5 @@
         user: openstack
         password: ${_param:rabbitmq_openstack_password}
         virtual_host: '/openstack'
+      sink:
+        listener_pool_name: 'designate-sink'