Bug 18989: (QA follow-up) Make Koha::Biblio->hidden_in_opac aware of OpacHiddenItemsH...

Bug 18989: (QA follow-up) Make Koha::Biblio->hidden_in_opac aware of OpacHiddenItemsHidesRecord

This patch makes the method aware of the new syspref. It will only eval
the rules against items if the OpacHiddenItemsHidesRecord syspref is
set.

Tests are added to reflect this.

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

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>