CI: fix race condition in kolla-ansible-host-vars role tests

A temporary file is removed by multiple test hosts, which all have
connection=local. This leads to a race between multiple executions of
the file module on localhost.

Add run_once.

Change-Id: I976122f72bdca7f91cbfcd81fca431b81a6b6aef

ansible/roles/kolla-ansible-host-vars/tests/test.yml

@@ -140,6 +140,7 @@
           file:
             path: "{{ temp_path }}"
             state: absent
+          run_once: true
 
         - name: Refresh the inventory
           meta: refresh_inventory