python/qemu/machine: use socketpair() for QMP by default

python/qemu/machine: use socketpair() for QMP by default

When no monitor address is given, establish the QMP communication through
a socketpair() (API is also supported on Windows since Python 3.5)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20230111080101.969151-4-marcandre.lureau@redhat.com
[Resolved conflicts, fixed typing error. --js]
Signed-off-by: John Snow <jsnow@redhat.com>
(cherry picked from commit bd4c0ef409140bd1be393407c04005ac077d4574)
(Mjt: this fixes quite a few qemu iotests which was probably racing somewhere)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>