test: start vhost-user reconnect test

This is a simple reconnect test, that simply checks if vhost-user
reconnection is possible and restore the state. A more complete test
would actually manipulate and check the ring contents (such extended
testing would benefit from the libvhost-user proposed in QEMU list to
avoid duplication of ring manipulations)

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