guest-overlay: make squash only once

guest-overlay/handlers/main.yml

+---
+# file: roles/guest-overlay/handlers/main.yml
+
+- name: restart kdm
+  service: name=kdm state=restarted

guest-overlay/tasks/main.yml

@@ -40,6 +40,7 @@
 
 - name: ensure the squasfs is created
   local_action: command mksquashfs "{{ role_path }}/files/provision" "{{ role_path }}/files/provision.squashfs"
+  run_once: True
   tags:
     - guest-overlay
     - squashfs