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[1] will most likely merge in its current shape or something very
close to it. It adds a `migration` positional argument to the
finish_revert_migration() virt driver method. `migration` is the, err,
migration that's being reverted.

If you have out of tree virt drivers, please update them to match this
new method signature.

Thanks!

[1] https://review.opendev.org/#/c/668631/