Correct playbook selection is now done automatically using
external_update_tasks and external_upgrade_tasks. The
CephAnsiblePlaybook is still usable and highest priority if set to
something else than the default. It can also be set to [] to
completely skip ceph-ansible playbook execution.
Closes-Bug: #1783949
Change-Id: If7955b31eda432dd61331281ad3d8f25a335fdfe
Depends-On: Ifdf5f1175849f79b98c76b4bcdef2a70f8f1fedb
20f614ba9a