Add SSH key to user "debug" during disk-install phase

* Avoid adding SSH authorized key for user "core" during the disk
install, so that terraform apply cannot SSH until post-install

bare-metal/container-linux/pxe-worker/ssh.tf

@@ -1,5 +1,5 @@
 # Secure copy kubeconfig to all nodes to activate kubelet.service
-resource "null_resource" "copy-kubeconfig" {
+resource "null_resource" "copy-secrets" {
   count = "${length(var.worker_names)}"
 
   connection {