Bug 22749: Regression tests for Koha::Item->hidden_in_opac

Bug 22749: Regression tests for Koha::Item->hidden_in_opac

This patch introduces regression tests for Koha::Item->hidden_in_opac to
verify it is not considering the hidelostitems syspref when determining
if an item should be hidden (per policy) in the OPAC.

To test:
- Apply this patch
- Run:
  $ kshell
 k$ prove t/db_dependent/Koha/Item.t
=> FAIL: Tests fail!

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>