rpm: py3-only for Fedora and EPEL 8+
rpm: py3-only for Fedora and EPEL 8+

We cannot build Python 2 on Fedora 31+ any more because that distro does
not have all the py2 dependencies.

Build Python 2 on el7 only. For everything else (Fedora and RHEL 8+),
build Python 3-only.

ktdreyer/errata-tool,red-hat-storage/errata-tool,red-hat-storage/errata-tool,ktdreyer/errata-tool