Followup on I91e5c1840ace8f567daf462c4eb3ec1f0c503823

When+run_once do not play nicely. [1]
The general workaround is to use include_tasks. [2]
However, it is very unlikely user wishes to run this role
without having any pacemaker nodes so the simplification that we
use throughout the Kolla Ansible code should be enough.

[1] https://github.com/ansible/ansible/issues/11496
[2] https://github.com/ansible/ansible/issues/11496#issuecomment-412936547

Change-Id: Ifaf64e3d9d89b2ec36a883fb7458556745b64802