I was finally able to attach ISO Domain to Datacenter after moving all Datacenter's
Storage Domains and Hosts to MAINTAINANCE except on the Host where I was creating the ISO
Domain.
It looks like a bug on oVirt that didn't allow to simply add a ISO Domain after all
other hosts and Data Domains has been previously added to my Datacenter. However, I'm
glad I was finally able to attach the ISO Domain to my Datacenter.
Thanks for everyone assistance