Add refreshonly to 'upgrade_subunit2sql_db'

This commit adds refreshonly to the 'upgrade_subunit2sql_db' exec.
The problem without this set is that subscribing to the Pip package
generates an event on each puppet refresh, which causes the db-manage
utility to run a migration update every 15 min, which is far from
ideal. Setting refreshonly means that the command is only run when
the resource changes, in this case when a new package version is
installed, which is the desired behavior.

Change-Id: Ib77d68f19edbf48a8d8cf4e757dbfb6463f1c6bb

manifests/server.pp

@@ -31,5 +31,6 @@ class subunit2sql::server (
     command     => 'subunit2sql-db-manage --config-file /etc/subunit2sql.conf upgrade head',
     path        => '/usr/local/bin:/usr/bin:/bin/',
     subscribe   => Package['subunit2sql'],
+    refreshonly => true,
   }
 }