Comment 4 for bug 1781286

OK looking at the stacktrace I see it's not the '_destroy_build_request' call that's blowing up on reschedule, it's the up-call to get the availability zone for the next chosen host from the list of alternates:

And if an AZ is not requested during server create, we are free to move the instance to another AZ during reschedule. So it seems we've fallen into a dreaded up-call hole here that needs to be tracked: