ci, docker: update CentOS and OpenSUSE Python to non-EOL versions

ci, docker: update CentOS and OpenSUSE Python to non-EOL versions

Python 3.6 is at end-of-life.  Update the libvirt-ci module to a
version that supports overrides for targets and package mappings;
this way, QEMU can use the newer versions provided by CentOS 8 (Python
3.8) and OpenSUSE 15.3 (Python 3.9).

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit d639cf79783a1eba349b7705e0fb270fa76118a4)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>