mingw: Use Python 3 for building
While RHEL / CentOS are still using Python 2 for the time being,
Fedora has already switched to Python 3 as the default Python
interpreter a while ago, so on that OS it doesn't make sense to
drag in Python 2 anymore.
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>