Fix issue in the priority/multifactor plugin where on a slurmctld restart

more time than should be allowed would be accounted for.

This only happened on jobs in the completing state when the slurmctld
was shutdown.

This will also be enhanced in 17.02 as the job's end_time_exp is not
stored which is needed to determine if the job has already been through
the decay_thread at end of job.

Bug 3162