[#87][#129] delete old logs once a job finishes/errors

Change log deletion so that each job cleans up it's old logs instead of
update_activities deleting the logs first.

Delete old logs of "job iatilib.update_{job_type}" when that job_type
finishes. If an exception occurs in that job_type, clean up the old logs
before logging as well to prevent logging the same error over and over
again.