[Merge] ~philroche/livecd-rootfs/+git/livecd-rootfs:bugfix/ubuntu-server-live-image-build-failures-return-code into livecd-rootfs:ubuntu/master

[Michael Hudson-Doyle]

Review: Approve

I think my feelings about shell scripts are on record
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https://code.launchpad.net/~philroche/livecd-rootfs/+git/livecd-rootfs/+merge/459376
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