audit/cleanup for upgrade status management

[joel-bluedata]

Part of issue #588.

The status management is spread out quite a bit, although I do recognize that there are places where it's easier to determine that a status change is needed.

As the branch stands:

• top-level cluster handler manages status.app and status.upgradeInfo
• statefulset reconciliation manages setting per-role status to upgrading/rollingback
• creating-member handler manages setting per-member status to upgrading/rollback
• creating-member handler also manages setting per-role and per-member status to upgraded/rolledback

There's a logic in that structure, but I think we should at least consider whether we can push the role status management into syncClusterRoles, since having status management in the executor package is the only part which really itches me.

I'm also still dubious about the need to have upgradingMembers status at the role-status level, and we don't seem to be making use of the image value stored in that map... but I'll suspend further worrying about that until we're sure that issue #594 is resolved.