Werk #13812: KUBE kube_cpu use latest cpu usage value when no new data is available

The check returned a 0 cpu usage value when the Kubernetes special agent was polled too frequently. This werk fixes this behaviour and returns the last reported usage value for a time interval of 60 seconds if no new data is available from the agent. If the last reported value is older than 60 seconds than the usage value will be omitted.

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