QEMU supports socket chardevs that establish connections like a server
or a client. The QEMUMonitorProtocol class only supports connecting as
a client. It is not possible to connect race-free when launching QEMU
since trying to connect before QEMU has bound and is listening on the
socket results in failure.
Add the QEMUMonitorProtocol(server=True) argument to bind and listen on
the socket. The QEMU process can then be launched and connects to the
already existing QMP socket without a race condition: