directories in this folder should be named:
  rhel-%{rhel}
  fedora-%{fedora}
  ...
and are in SPEC files appended to config. E.g
  host-override/fedora-%{fedora}/fedora-31-x86_64.cfg
is appended to
  mock/fedora-31-x86_64.cfg
if we are building for fedora-%{fedora}
