Lower sql_idle_timeout to 180s

HAProxy has default timout 300s so we need to lower it bellow this limit
by default.

Change-Id: I95c1f0f64dba16c086075246944ba8d1d5471ae3
diff --git a/metadata/service/server/single.yml b/metadata/service/server/single.yml
index d5c4cf2..8ba73ca 100644
--- a/metadata/service/server/single.yml
+++ b/metadata/service/server/single.yml
@@ -23,7 +23,7 @@
         name: barbican
         user: barbican
         password: ${_param:mysql_barbican_password}
-        sql_idle_timeout: 1200
+        sql_idle_timeout: 180
       identity:
         engine: keystone
         host: ${_param:single_address}