Bug 28097: Mock finesModes to disable recalculation

Bug 28097: Mock finesModes to disable recalculation

Since bug 8338 the recalcuated zero amount fine is subsequently removed
in _FixOverduesOnReturn which causes this test to fail if finesMode is
'production' and 'CalculateFinesOnReturn' is enabled.

Perhaps we should be 'VOID'ing fines rather than completely deleting
them, but that's a question for another day.

Test plan
1/ Enable finesMode in the staff client
2/ Run the test and watch it fail
3/ Apply the patch
4/ Run the test and watch it pass

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>