Log with cell.uuid if cell.name is not set
Log with cell.uuid if cell.name is not set

CellMapping.name is optional but uuid is not, so if
name isn't set we should use the uuid when logging the
cell that we're pulling instances from when listing
instances.

Change-Id: I684d04ceb121d4f32fb465388f2f304a92f321a3
Related-Bug: #1669473

jianghuaw/nova,klmitch/nova,jianghuaw/nova,Juniper/nova,klmitch/nova,vmturbo/nova,phenoxim/nova,klmitch/nova,Juniper/nova,rahulunair/nova,mikalstill/nova,rahulunair/nova,gooddata/openstack-nova,Juniper/nova,mikalstill/nova,Juniper/nova,mahak/nova,jianghuaw/nova,phenoxim/nova,jianghuaw/nova,rahulunair/nova,rajalokan/nova,vmturbo/nova,gooddata/openstack-nova,rajalokan/nova,mahak/nova,rajalokan/nova,gooddata/openstack-nova,openstack/nova,mahak/nova,vmturbo/nova,vmturbo/nova,mikalstill/nova,openstack/nova,gooddata/openstack-nova,rajalokan/nova,klmitch/nova,openstack/nova