Described how we decide which host platforms to support for libvirt,
which in turn makes it easier to decide when a platform / software
version can be dropped.
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>