Allow configuration of sql_idle_timeout

This helps to avoid `MySQL server has gone away` errors.

Change-Id: I62082a3b07d66ddd97b1cde3ad84ee308f36313e
diff --git a/metadata/service/server/single.yml b/metadata/service/server/single.yml
index 91d1b2f..d5c4cf2 100644
--- a/metadata/service/server/single.yml
+++ b/metadata/service/server/single.yml
@@ -23,6 +23,7 @@
         name: barbican
         user: barbican
         password: ${_param:mysql_barbican_password}
+        sql_idle_timeout: 1200
       identity:
         engine: keystone
         host: ${_param:single_address}