remove core-os.net from default install sources
core-os.net appears to now be a dead URL with no A records for the domain.
With the move to Red Hat and Atomic / core-os Atomic, would it be sensible to make a minor change and drop core-os.net from the default installation media sources ?
Happy to make the change and make a PR just wanted to gather feedback if it was worth it ? could also be good to start prepping in development branches for replacing core OS by default ?