Problem: Exceptions from the doom plugin do not specify what
job failed.  It can be confusing to users which job failed amongst
multiple in a batch job, or if the broker from a batch job itself
failed.

Add the job executable name to the doom exception outputs.

Fixes flux-framework#6357

Problem: In a batch job, it may be difficult to discern which
job had an exception.

When flux job attach outputs an exception, also output the jobid
of the job.

Update tests in t2608-job-shell-log.t and t2304-sched-simple-alloc-check.t
for change in expected output.