python/qmp: switch qmp-shell to AQMP

We have a replacement for async QMP, but it doesn't have feature parity
yet. For now, then, port the old tool onto the new backend.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>