[JENKINS-22639] Don't record changes to AbstractCloudSlaves or Ephemeral Nodes

This can result in high load when there are nodes coming online and offline quickly.
I have been working on this recently in the context of long-running builds and concluded that `EphemeralNode` should simply be avoided whenever possible. The implication is that a plain `AbstractCloudSlave` is also something that probably has no valuable configuration and should not be tracked. Therefore I agree with merging this PR as it stands.