improve error message when schedd too busy to respond to jobsub_rm
See INC000001024153. The error message returned to the user is something along the lines of 'condor_rm cant find the address of schedd jobsub01.fnal.gov'. The developers and most 'old hands' know this to be a symptom of the schedd being too busy to reply to jobsub commands, but it is not helpful at all to someone who has never seen the behavior before.
Intercept this error, report something more helpful and suggest a workaround.