Comment 6 for bug 1100545

verified using the test above, but instead of using the deb, patched to use proposed like:
sudo ./bi/mount-callback-umount patched.img.dist -- \
    env LANG=C chroot MOUNTPOINT sh -ec '
       rel=$(lsb_release -sc)
       echo "deb http://archive.ubuntu.com/ubuntu $rel-proposed main" > \
            /etc/apt/sources.list.d/$rel-proposed.list
       apt-get update -q -y
       apt-get install cloud-init -q -y'