libqtest: add qmp_async Add qmp_async, which lets us send QMP commands asynchronously. This is useful when we want to send commands that will trigger event responses, but we don't know in what order to expect them. Sometimes the event responses may arrive even before the command confirmation will show up, so it is convenient to leave the responses in the stream. Signed-off-by: John Snow <jsnow@redhat.com> Message-id: 1426018503-821-5-git-send-email-jsnow@redhat.com