Configure zk\d to act as a cluster

You have to tell the zk servers what servers belong to the cluster to
have them act as a cluster. Currently all our servers are in mode
standalone as they do not know about the other servers.

Fix this by configuring the three servers as servers 1, 2, and 3 in the
zk config.

Change-Id: I985ac7387744498058f99859eb8445f885b8bbcc

manifests/site.pp

@@ -677,6 +677,11 @@ node /^static\d*\.openstack\.org$/ {
 
 # Node-OS: xenial
 node /^zk\d+\.openstack\.org$/ {
+  $zk_cluster_members = {
+    1 => 'zk01.openstack.org',
+    2 => 'zk02.openstack.org',
+    3 => 'zk03.openstack.org',
+  }
   class { 'openstack_project::server': }
 
   class { '::zookeeper':