This fixes the message (node name and "cluster-scoped" were switched) and
simplifies the VAP:
- a single matchCondition short circuits completely unless they're a user
we care about
- variables to extract the userNodeName and objectNodeName once
(using optionals to gracefully turn missing claims and fields into empty strings)
- leaves very tiny concise validations
Co-authored-by: Jordan Liggitt <liggitt@google.com>