RFE: white/black list of nodes for system status degraded

[engelmi]

Please describe what you would like to see

In #603, a status property has been introduced to reflect the system status. As discussed, it might be desirable to be able to specify which nodes can cause the degraded status - e.g. if one node has a brittle connection or is expected to be offline sometimes.

Please describe the solution you'd like

Extending the configuration for bluechi-controller by a field to define which node names (subset of AllowedNodeNames) are causing or not causing a degraded status.
Note: No changes shall be made for the down status.