Using dns domain instead of cluster name for coredns, incase they differ

roles/kubernetes-apps/ansible/templates/coredns-config.yml.j2

@@ -11,7 +11,7 @@ data:
     .:53 {
         errors
         health
-        kubernetes {{ cluster_name }} in-addr.arpa ip6.arpa {
+        kubernetes {{ dns_domain }} in-addr.arpa ip6.arpa {
           pods insecure
           upstream /etc/resolv.conf
           fallthrough in-addr.arpa ip6.arpa