Commits f18390e8 and eed76f85 modified the stepd so that if the
stepd encountered an unkillable step timeout that the stepd would just
exit the stepd. If the stepd is a batch step then it would reply back
to the controller with a non-zero exit code which will drain the node.
But if an srun allocation/step were to get into the unkillable step
code, the steps wouldn't let the waiting srun or controller know about
the step going away -- leaving a hanging srun and job.

This patch enables the stepd to notify the waiting sruns and the ctld of
the stepd being done and drains the node for srun'ed alloction and/or
steps.

Bug 5164