criu: Write pidfile later
criu: Write pidfile later

Next patch will put non-root task's PID into it, so this
one is preparatory. But, as a bonus, we remove the need
to unlink ths pid file in case of error :)

Risk -- scripts might want to have pidfile, but we already
have CRTOOLS_ROOT_PID environment in them for such cases.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

KKoukiou/criu-remote,efiop/criu,KKoukiou/criu-remote,efiop/criu,eabatalov/criu,KKoukiou/criu-remote,efiop/criu,eabatalov/criu,efiop/criu,eabatalov/criu,efiop/criu,efiop/criu,eabatalov/criu,KKoukiou/criu-remote,KKoukiou/criu-remote,eabatalov/criu,eabatalov/criu,KKoukiou/criu-remote