[Merge] ~mwhudson/livecd-rootfs/+git/livecd-rootfs:expand-task into livecd-rootfs:ubuntu/master

[Steve Langasek]

Review: Approve

To test this, I want to run image builds with and without -proposed in parallel, and examine the resulting manifest files.

We should upload this only after mantic image builds have been turned on and passed once, so that we CAN establish a baseline before this change.
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https://code.launchpad.net/~mwhudson/livecd-rootfs/+git/livecd-rootfs/+merge/425047
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