BibSched: problem parsing task CLI options

* Fixes an issue introduced in 9369361849c6a21fec164fb10abb999ebc3e3748
  that caused certain CLI arguments (like -l) to be mismatched due to
  comparison against a string instead of a tuple of strings. (fixes #1330)

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