[contrib/terraform/openstack] Add supplementary node groups

* Add supplementary node groups

  To add additional ansible groups to the k8s nodes, such as
  `kube-ingress` for running ingress controller pods. Empty by default.

contrib/terraform/openstack/variables.tf

@@ -116,3 +116,8 @@ variable "supplementary_master_groups" {
   description = "supplementary kubespray ansible groups for masters, such kube-node"
   default = ""
 }
+
+variable "supplementary_node_groups" {
+  description = "supplementary kubespray ansible groups for worker nodes, such as kube-ingress"
+  default = ""
+}