Bug 28254: Add 'override' parameter to Koha::Hold->set_pickup_location

Bug 28254: Add 'override' parameter to Koha::Hold->set_pickup_location

This patch adds a new parameter to the method. If passed+true it makes
the method skip the pickup validation test.

Tests and POD added for this change.

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

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>