In case of keystone-fernet-setup job rerun (delete and create),
fernet tokens are recreated. Which leads to ongoing openstack request
fail.
keystone-manage fernet_setup is idempotent, let's make the
keystone-fernet-setup job idempotent as well.
Change-Id: I62e741fe5192b7a0018bc84ccdac1ea5311a1e03