introduce step accounting for a Cray.

This is needed if the munge deamon is under very heavy load
(e.g. with 1000 slurmd daemons per compute node).

slurmctld restart.

Modify sbast logic to continue when slurmd daemon restarts

Previously a file transmission in progress would be aborted when
any of the slurmd daemons restarted. Now it reconnects, revalidates
the credential, and resumes file transmission.

midplane having a bad nodeboard previously used for passthrough when
the same midplanes were used in a block with a torus connection in that
dim.