Fixing upgrade script (Bug #1350254)

Problem with ensure_record_exists checking nextrun column will break
things when adding new cron line to cron table.

This is due the the nextrun not being null after it has run.

Change-Id: I1f674cbc842a3e061224bf996cc0267b09018f55
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>