Comment 32 for bug 1576692

verified with:
printf "#cloud-config\npackages: [postgresql, samba, postfix]\n" > user-data
n=x1
lxc launch ubuntu-daily:xenial $n
sleep 10
lxc exec $n -- sh -c '
    p=/etc/apt/sources.list.d/proposed.list
    echo deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc)-proposed main > "$p" &&
    apt-get update -q && apt-get -qy install cloud-init'

lxc file push - $n/etc/cloud/cloud.cfg.d/update.cfg < user-data

## clean it out so next is first boot.
lxc exec $n -- sh -c '
  cd /var/lib/cloud && for d in *; do [ "$d" = "seed" ] || rm -Rf "$d"; done
  rm -Rf /var/log/cloud-init*'

lxc exec $n reboot
lxc exec $n -- tail -f /var/log/cloud-init-output.log