Comment 5 for bug 1028501

I verified this (close to it) on a precise instance:
* enable proposed
  $ m=http://archive.ubuntu.com/ubuntu
  $ r=$(lsb_release -sc)
  $ echo "deb $m $r-proposed main" |
     sudo tee /etc/apt/sources.list.d/$r-proposed.list
* update cloud-init
  $ sudo apt-get install cloud-init
* hack dpkg so '--print-architecture' lies
  $ sudo mv /usr/bin/dpkg /usr/bin/dpkg.real
  $ sudo tee /usr/bin/dpkg <<"EOF"
  #!/bin/sh
  [ "$1" = "--print-architecture" -a $# -eq 1 ] && { echo "armhf" && exit; }
  exec "$0.real" "$@"
  EOF
  $ sudo chmod 755 /usr/bin/dpkg
* re-run the apt-update-upgrade config module
  $ sudo cp -a /etc/apt/sources.list /etc/apt/sources.list.save
  $ sudo cloud-init-cfg apt-update-upgrade always
* now, /etc/apt/sources.list has 'ports.ubuntu.com' in it
  and /var/log/cloud-init.log mentions it used it:

  $ grep mirror.info /var/log/cloud-init.log
  Dec 12 21:58:33 ip-10-117-77-88 [CLOUDINIT] cc_apt_update_upgrade.py[DEBUG]: mirror info: {'security': 'http://ports.ubuntu.com/ubuntu-ports', 'primary': 'http://ports.ubuntu.com/ubuntu-ports', 'mirror': 'http://ports.ubuntu.com/ubuntu-ports'}
  $ grep "^deb " /etc/apt/sources.list | head -n 3
  deb http://ports.ubuntu.com/ubuntu-ports precise main
  deb http://ports.ubuntu.com/ubuntu-ports precise-updates main
  deb http://ports.ubuntu.com/ubuntu-ports precise universe