python/machine: close sock_pair in cleanup path

python/machine: close sock_pair in cleanup path

If everything has gone smoothly, we'll already have closed the socket we
gave to the child during post_launch. The other half of the pair that we
gave to the QMP connection should, likewise, be definitively closed by
now.

However, in the cleanup path, it's possible we've created the socketpair
but flubbed the launch and need to clean up resources. These resources
*would* be handled by the garbage collector, but that can happen at
unpredictable times. Nicer to just clean them up synchronously on the
exit path, here.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Ani Sinha <anisinha@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20230928044943.849073-3-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>