Since version 2.12.0 AF_UNIX socket created for QMP exchange is not
deleted on instance shutdown.

This is due to the fact that function qio_channel_socket_finalize() is
called after qio_channel_socket_close().

Signed-off-by: Pavel Balaev <mail@void.so>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>