[Openstack] Add security groups not managed by terraform (#6865)

* add custom sec groups

* make sure groups are applied only when created

* fix spacing

contrib/terraform/openstack/variables.tf

@@ -246,3 +246,10 @@ variable "k8s_nodes" {
   default = {}
 }
 
+variable "extra_sec_groups" {
+  default = false
+}
+
+variable "extra_sec_groups_name" {
+  default = "custom"
+}