Change --engine-url for --fqdn

[aesteve-rh]

Current argument --engine-url doesn't make sense. https://[fqdn] is not an engine url.

It should either ask just for fqdn, or “engine url” should be https://[fqdn]/ovirt-engine, or ask for engine api url and that would be https://[fqdn]/ovirt-engine/api. But as it stands right now it's misleading.