The test case used to work only on Fedora 33. This patch introduces
support for all future Fedoras and RHEL 8.
It uses a fair bit of magic because it needs to dynamically discover if
a RHEL runner uses the rhel-8.json or the rhel-8-beta.json repository
override. Furthemore it needs to discover a redirection URL, if any, of
the repository override to correctly configure HTTP proxy.