Always pass 'NUMACell.siblings' to _pack_instance_onto_cores'
Always pass 'NUMACell.siblings' to _pack_instance_onto_cores'

Now that we're populating the aforementioned attribute with cores that
don't have siblings, we don't need to continue creating imitation lists
of "siblings".

Change-Id: Ia371684dd9f821f214c6e023845875021848ca0a
Related-Bug: #1744965

mahak/nova,mikalstill/nova,klmitch/nova,mahak/nova,rahulunair/nova,openstack/nova,openstack/nova,gooddata/openstack-nova,mahak/nova,rahulunair/nova,gooddata/openstack-nova,gooddata/openstack-nova,openstack/nova,mikalstill/nova,phenoxim/nova,mikalstill/nova,klmitch/nova,klmitch/nova,phenoxim/nova,gooddata/openstack-nova,klmitch/nova,rahulunair/nova