qemu: Formally deprecate support for qemu < 2.11

qemu: Formally deprecate support for qemu < 2.11

As of May 7 2021, rhel-8 will be out for two years, which means we no
longer have to support rhel-7 ancient qemu.

QEMU versions in our supported distros:

 RHEL-8: 2.12
 Debian Stable: 3.1
 OpenSuse LEAP 15.0 (SLES15 GA): 2.11
 OpenSuse LEAP 15.2: 4.2
 Ubuntu (Bionic): 2.11
 Ubuntu (Focal): 4.2

This means we can bring up the minimum supported version to 2.11.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>