python/qmp: switch qemu-ga-client to AQMP

python/qmp: switch qemu-ga-client to AQMP

Async QMP always raises a "ConnectError" on any connection error which
houses the cause in a second exception. We can check if this root cause
was python's ConnectionError to determine a fairly similar condition to
the original error check here.

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