Bug 18635: Unit tests

Bug 18635: Unit tests

I also adjust a few tests that assume value of $nb_of_patrons to not
rely on existing datas

To test:
1 - Apply this patch only
2 - Prove t/db_dependent/Koha/Patrons.t
3 - Tests fail
4 - Apply other patch
5 - Tests pass

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit ac0f3b880a4220317ddde107c508c32f75b09aa1)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>