Code review comment for lp:~rvb/maas/add-fqdn

According to the new strategy the two of us just talked about, I just changed the 'fqdn' property:
- if the nodegroup manages DNS: strip the domain part out of the hostname (if any) and then use nodegroup.name as the domain
- if the nodegroup does not mange DNS: just return whatever is in the 'hostname' field.