Rework WaitUntilReady

Suggested release note:

The waitUntilReady method is now more aggressive about retrying failed pings. Also, waiting for a desired state of DEGRADED no longer fails when the client is fully connected to the cluster.

Investigate how WaitUntilReady could be improved.

Specifically:

1. Rework the pacemaker. The current "wait some more" logic is odd, and results in redundant node health checks. Instead of being driven by a flux interval(), perhaps we could use a retry operator.
2. Investigate whether pings are currently being retried, and look into why we're consulting the diagnostic results – should ping alone be sufficient?