Bug 21910: Koha::Library::Groups->get_search_groups should return the groups

Bug 21910: Koha::Library::Groups->get_search_groups should return the groups

To test:
 1 - Add a library group (Admin->Library groups)
 2 - Enable use as an opac and staff search limit
 3 - Add some libraries to the group
 4 - Visit advanced search on staff and opac
 5 - Note the dropdown has as many empty rows as there are libraries
  in the group
 6 - Apply patch, restart all the things
 7 - Visit staff and opac advanced search
 8 - Confirm the group dropdowns are correct
 9 - Enable OpacMastheadLibraryPulldown
10 - Ensure the dropdown on opac shows groups correctly
11 - Confirm earchign groups works from all three locations
12 - prove -v t/db_dependent/LibraryGroups.t

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>