[Merge] ~kxuan/livecd-rootfs:add-sector-size into livecd-rootfs:ubuntu/master

[Łukasz Zemczak]

Review: Approve

I guess this should be fine. One thing to remember is that SECTOR_SIZE won't be able to be used via livefs builds until we get relevant changes to launchpad-buildd. But that can be another story.
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https://code.launchpad.net/~kxuan/livecd-rootfs/+git/livecd-rootfs/+merge/464882
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