investigate possible upgrade/rollback race

[joel-bluedata]

Part of issue #588.

If you trigger an upgrade, then immediately trigger a rollback, I'm concerned about some possible race conditions in the pod statuses and notifications. handleCreatingMembers will assume PodRollingBack status but maybe it's possible that the pod is coming up at that moment with the image from the upgrade? Rather than rely on kdcluster status here to see what is going on, we might have to actually check the pod image.