Bug 13606: Add tests and fix existing ones

Bug 13606: Add tests and fix existing ones

Some tests were wrong and not executed in a transaction.
Lot of sessions were created in DB because the session was never
flushed.

TEST PLAN
---------
$ mysql ...
> delete from sessions;
^Z
$ prove -v t/db_dependent/BackgroundJob.t
...
$ fg
> select id from sessions;
-- There will be lots of ids (10, if I recall)
^Z
$ git bz apply 13606
...
$ prove -v t/db_dependent/BackgroundJob.t
...
$ fg
> select * from sessions;
-- there should only be the one orphaned job.
   You can tell it is correct by the "making new job".
> quit

Run the koha-qa test tools.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>