Werk #10475: Azure Checkplugins: Go to stale state if info is missing

Previously a service resulting from one of the Azure checkplugins went to UNKOWN if the corresponding data was not found in the agent output, as is common for many checkmk services. Unfortunately, this happens too often to be usefull, as the Azure API appears to not allways report the full data. Now the affected services go to a stale state instead.

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