Fix glusterfs client fallback servers

Change-Id: Ida4a1272d29392dd90b4901ece185e85a5db0302
diff --git a/glusterfs/client/volume/prometheus.yml b/glusterfs/client/volume/prometheus.yml
index 2b2b7db..49145d3 100644
--- a/glusterfs/client/volume/prometheus.yml
+++ b/glusterfs/client/volume/prometheus.yml
@@ -7,4 +7,4 @@
         prometheus:
           path: /srv/volumes/prometheus
           server: ${_param:prometheus_glusterfs_service_host}
-          opts: 'defaults'
+          opts: "defaults,backup-volfile-servers=${_param:cluster_node01_address}:${_param:cluster_node02_address}:${_param:cluster_node03_address}"