online schema change: _very_ carefully clean up, and prompt before each step.
online schema change: _very_ carefully clean up, and prompt before each step.

 - Wait for all nodes to be running
 - ptosc_verify_continue: Replace with agree()
 - verify there are no triggers before we drop the user.
 - verify the old and tmp tables don't exist before trying to use them.
 - clean up crufty tables before starting

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