We could also make `LUKSDevice.size` grab its value from the parent/slave so it
doesn't need to store its own target size.
I would rather make the convention to schedule actions on both the luks format and the
luks device. The action on the luks device would be a no-op, but it makes it much cleaner
than having to remember which of the two you're supposed to schedule.
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To view this pull request on github, visit
https://github.com/rhinstaller/blivet/pull/308