zdtm/socket_aio: add a synchonization between processes

The test has to do nothing during c/r.

======================= Run zdtm/static/socket_aio in ns =======================
Start test
./socket_aio --pidfile=socket_aio.pid --outfile=socket_aio.out
Run criu dump
Run criu restore
5: Old maps lost: set(["7f0a5188a000-7f0a5188f000 ['rw-p']"])
5: New maps appeared: set(["7f0a51884000-7f0a5188f000 ['rw-p']", "7f0a51883000-7f0a51884000 ['---p']"])
Send the 9 signal to  97
Wait for zdtm/static/socket_aio(97) to die for 0.100000

Reported-by: Mr Jenkins
travis-ci: success for zdtm/socket_aio: add a synchonization between processes
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>