test: libcriu: switch to using swrk instead of service

As our tests serve as an example for people on how to preferably
use criu, we need to also switch to swrk.

Signed-off-by: Ruslan Kuprieiev <rkuprieiev@cloudlinux.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>