BibUpload: task error messages

• Error message would not display in bibsched

BibUpload: reworks error handling

• Shifts responsibility of setting error status back to bibtask.py so we can handle properly the error reporting in case the submitter uses --email-logs-to. (closes #1449)

Co-authored-by: Samuele Kaplun <samuele.kaplun@cern.ch>