Bug 1953: updating bad unit test for C4::Items::GetItemsForInventory

Bug 1953: updating bad unit test for C4::Items::GetItemsForInventory

The tests I wrote for C4::Items::GetItemsForInventory confused the differences
between biblionumber and itemnumber. That wasn't uncovered on my limited test
database, but I uncovered it later.

This fixes that problem by populating a $self->{'items'} list with details of any items
added by KohaTest::add_biblios. Then, tests can probe there for the details of items
they should expect to find when searching.

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Joshua Ferraro <jmf@liblime.com>