Have slaunch's return be the maximum task return code.

Fix and revamp test15.9.

Change logging level of a message in slaunch.

needs to print out some tast status messages.

Change slaunch's short --quiet option to -q from -Q.

Add SLURM_STEP_CTX_JOBID which is getable from the step context.

The "pending_callback" is called when the allocation cannot be granted
immediately.  This allows the "Pending job allocation" message to be
printed in salloc.c rather than being burried in the API code.

exception (documented in the man page) is SIGHUP, which will have salloc
revoke the allocation immediately.  The SIGHUP behavior should avoid users
leaving allocations lying around when they ungracefully log out of a machine.

This eliminates a bunch of new errors for RPCs like SRUN_JOB_COMPLETE
which can fail if the srun has already terminated before the 
messages gets sent from slurmctld.

Rely upon slurmd and srun to tell us of the step's completion.

functionality.

There is a test for slaunch signal handling though.