Add keystone cron container to run token_flush
Add keystone cron container to run token_flush

The token-flush cron job is created in /var/spool/cron/keystone
by puppet. This patch creates a cron container to run that
in an environment where it has access to keystone.conf
and the keystone-manage binaries.

Change-Id: Ie305ee9990657c66938250d1d6e19fef94675997
Partial-bug: 1701254

dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates