Werk #925: ps: improved/fixed calculation of CPU utilization (linux)

Previously, the CPU utilization value was taken from the output pcpu from the ps command. This value didn't reflect the exact utilization since the last check because its definition is

CPU usage is currently expressed as the percentage of time spent running
during the entire lifetime of a process.  This is not ideal, and it does not
conform to the standards that ps otherwise conforms to.  CPU usage is
unlikely to add up to exactly 100%.

The evaluation of the pcpu field has been removed and got replaced by the field cputime, which reflects the number of cpu seconds since program start. With the cputime we are able to determine the correct value.

To utilize this new calculation method, you need to update the check_mk_agent on the target host. The ps check itself is able to handle both formats, pcpu and cputime.

Note: This bug only applied to hosts using the linux check_mk_agent

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