vhost-user-test: fix predictable filename on tmpfs vhost-user-test uses getpid to create a unique filename. This name is predictable, and a security problem. Instead, use a tmp directory created by mkdtemp, which is a suggested best practice. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>