Werk #13118: sentry_pdu, raritan_pdu_plugs: Fix parameter handling

The check plugins sentry_pdu and raritan_pdu_plugs both monitor the status of PDUs. In the discovery phase, both plugins store the current states of the discovered PDUs. The subsequently computed check results are based on a comparison of the discovered states with the current states of the PDUs. Both plugins did not handle unknown states properly.

Furthermore, users have the option to explicitly configure target states for the PDUs. In this case, the user-configured states are preferred over the discovered states. This mechanism was broken for sentry_pdu.

Finally, when updating Checkmk from 1.6 to 2.0 and also during updates within 2.0, the states discovered by the plugin sentry_pdu were lost.

To fix these issues, users have to re-discover the corresponding services "Plug ...". Note that for raritan_pdu_plugs, depending on the current configuration, a re-discovery might not be necessary, but we recommend it preemptively.

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