when run several tests simultaneousely it seem that some iptables
commands can intersect and if we do not wait xtables lock criu fails:

(00.009263)     Running iptables [iptables -t filter -A INPUT --protocol tcp --source 127.0.0.1 --sport 55074 --destination 127.0.0.1 --dport 8880 -j DROP]
Another app is currently holding the xtables lock. Perhaps you want to use the -w option?
(00.014367) Error (util.c:660): exited, status=4
(00.014416) Error (netfilter.c:88): Iptables configuration failed: Success
(00.014432) ----------------------------------------
(00.014461) Error (cr-dump.c:1297): Dump files (pid: 24) failed with -1

https://ci.openvz.org/job/CRIU/job/CRIU-virtuozzo/branch/criu-dev/3/Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Acked-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>