Setting up backend images for VCP VM's

This patchset is required by: #/c/25365/

Change-Id: I2aa73d3f16b10d2d7597a89f46fdeed6bf268661
diff --git a/salt/control/cluster/openstack_dns_cluster.yml b/salt/control/cluster/openstack_dns_cluster.yml
index 7f1dbb8..6fcc546 100644
--- a/salt/control/cluster/openstack_dns_cluster.yml
+++ b/salt/control/cluster/openstack_dns_cluster.yml
@@ -1,4 +1,7 @@
 parameters:
+  _param:
+    salt_control_xenial_image_backend: /var/lib/libvirt/images/backends/xenial.qcow2
+    openstack_dns_backend_image: ${_param:salt_control_xenial_image_backend}
   salt:
     control:
       size:
@@ -16,9 +19,11 @@
               name: ${_param:openstack_dns_node01_hostname}
               provider: ${_param:infra_kvm_node01_hostname}.${_param:cluster_domain}
               image: ${_param:salt_control_xenial_image}
+              backend: ${_param:openstack_dns_backend_image}
               size: openstack.dns
             dns02:
               name: ${_param:openstack_dns_node02_hostname}
               provider: ${_param:infra_kvm_node02_hostname}.${_param:cluster_domain}
               image: ${_param:salt_control_xenial_image}
+              backend: ${_param:openstack_dns_backend_image}
               size: openstack.dns