Sanity check to make sure job_list exists before restoring cache.
Better code to handle caching.  Followup to
9368ff2dd955c96759b634ec68f65cb9a1cf2594
Fix race condition is corner case with backup slurmctld.
With the backup slurmctld make sure we reinit beginning values in the
slurmdbd plugin.
NEWS for the last 2 commits