Escape use of '%' in cron entries.

The '%' has special meaning in cron. Escape the use of this character in
cron entries to allow these cron entries to run properly.

Change-Id: I049a8a2a4454f99aedb7fe3017db231b8a13e569
Reviewed-on: https://review.openstack.org/27294
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins