Bug 30181: (QA follow-up) Update BatchTest

Bug 30181: (QA follow-up) Update BatchTest

This patch updates t::lib::Koha::BackgroundJob::BatchTest to the new
style, and also removes a couple stray cases in which job_id was still
passed as a parameter.

Tests are rewritten a bit, so they actually test more of the behaviors.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/BackgroundJobs.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>