Return the zone_name when adding a zone with name_from_ip.

When adding a zone using the option name_from_ip, the user have
little control over the final name of the zone, and if this name
is to be used in further processing in a playbook it might lead to
errors if the inferred name does not match what the user wanted to.

By returning the actual inferred zone name, the name can be safely
used for other tasks in the playbook.