Do not abandon unreviewed changes

Change the review expiring logic to stop abandoning changes that have
not been reviewed.

Change-Id: I5b0a131fb8f3d2a83e71d5bfbb8729db8615db2e
Reviewed-on: https://review.openstack.org/31204
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins