Ensure that we run token-flush cron job under correct user.

Also remove creation of /var/log/keystone/keystone.log as it should be created correctly now.
Closes-bug: rhbz#1071674

Change-Id: I450d89d47527db101f56bf173062ba33ceb3b54d
Merge "Ensure that we run token-flush cron job under correct user."