zdtm: implement testing of --leave-stopped criu option
zdtm: implement testing of --leave-stopped criu option

Test does its checking both after dump and after restore.
Checking is done in the following way:
1. Check that every ps tree process is stopped or dead
2a. SIGKILL every ps tree process if checking after dump
2b. SIGCONT every ps tree process if checking after restore

Signed-off-by: Eugene Batalov <7a4372f440491fdba11e6e9c63b691b267a65e67@gmail.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote