Add collectd support

This also installs 2 additional packages (libdbd-mysql and
python-pymysql) that are required for running the collectd plugins.
diff --git a/metadata/service/slave/cluster.yml b/metadata/service/slave/cluster.yml
index 8f829b2..2432da6 100644
--- a/metadata/service/slave/cluster.yml
+++ b/metadata/service/slave/cluster.yml
@@ -1,5 +1,7 @@
 applications:
 - galera
+classes:
+- service.galera.support
 parameters:
   _param:
     galera_server_cluster_name: galeracluster
@@ -32,4 +34,4 @@
       - name: haproxy
         host: '%'
       - name: haproxy
-        host: ${_param:cluster_local_address}
\ No newline at end of file
+        host: ${_param:cluster_local_address}