tests: added listening socket migration test

This test is based on socket_aio. It's actually the same, except that socket
binding and listening is done before checkpointing and connection to socket is
done after migration.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>