These hooks opens inetsk.img, but it doesn't exist if
processes were pre-dumped.

travis-ci: success for test: skip pre-dump images in socket-tcp*.hook
Reported-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>