Fix --order when running under python3
Fix --order when running under python3

The --order options invokes some sorting comparision functions which are
no longer available under python3. Switch the sort cmp to cmp_to_key and
drop the usage of cmp.

Change-Id: I6f7bcc34d03c5fc398b3da1920dd3637cbe3d36b

openstack-packages/DLRN,openstack-packages/delorean,openstack-packages/DLRN,openstack-packages/delorean