tests: add a simple /vhost-user/multiqueue test

This test just checks that 2 virtio-net queues can be setup over
vhost-user and waits for them to be started.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
