Supporting a build platform beyond its end of life makes no sense.
Spell that out just to be clear.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200213084335.15100-1-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>