As of April 23 2022, Ubuntu 20.04 will be out for two years, which means
we no longer have to support Ubuntu 18.04 along with qemu-2.11 shipped
with it.

This then brings the minimum qemu version we have to support to
qemu-3.1:

   Debian 10/Stable: 3.1
 OpenSUSE Leap 15.3: 5.2
       Ubuntu 20.04: 4.2
    RHEL/Centos 8.4: 4.2

Next event in this space will be 2023/07/06 when Debian 11 will be out
for two years.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>