parallels: Move check of leaks to a separate function

We will add more and more checks so we need a better code structure
in parallels_co_check. Let each check performs in a separate loop
in a separate helper.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
Message-Id: <20230424093147.197643-10-alexander.ivanov@virtuozzo.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>