Bug 13319: Fix Koha::Acq::Order should set parent_ordernumber

Bug 13319: Fix Koha::Acq::Order should set parent_ordernumber

The tests highligh the problem: if the parent_ordernumber attribute is
not set on inserting an order, the object returned by the method does
not contain the value (undef).

Test plan:
Verify the tests are consistent and
    prove t/db_dependent/Acquisition/CancelReceipt.t
should return green.

You can also verify that receive partially an order and cancel the
receipt work as expected.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>