Werk #13757: Ps check on Linux: Handle processes with deleted cgroups

The ps (process) check on Linux was not able to handle processes with deleted cgroups. Such processes result in crashes such as "ValueError (invalid literal for int() with base 10: '...')"

The Linux ps check now handles such processes correctly. It appends "(deleted)" to the cgroup of the process, as is done by the ps command.

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