Python 3.5 is the oldest Python version available on our
supported build platforms, and Python 2 end of life will be 3
weeks after the planned release date of QEMU 4.2.0.  Drop Python
2 support from configure completely, and require Python 3.5 or
newer.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20191016224237.26180-1-ehabkost@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>