Checkmk Werk 7430: ps: fix empty output on older distros with cgroups

ID: 7430 Title: ps: fix empty output on older distros with cgroups Component: Checks & agents Level: 1 Class: Bug fix Version: 1.7.0i1 Werk #7420 used the column cgname to determine if a process belongs to a docker container. Unfortunately, the column is not available on older distros with cgroups like e.g. Ubuntu 16.04. To fix this issue the ps section now uses the cgroup column.