Comment 6 for bug 1666986

$ rel=yakkety
$ name=yakkety-1
$ lxc launch ubuntu-daily:$rel $name
$ lxc exec $name -- sh -c 'while ! [ -e /run/cloud-init/result.json ]; do echo .; sleep 1; done' </dev/null
$ lxc exec $name -- sh -e <<"EOF"
rel=$(lsb_release -sc)
line=$(awk '$1 == "deb" && $2 ~ /ubuntu.com/ {
  printf("%s %s %s-proposed main universe\n", $1, $2, rel); exit(0) };
  ' "rel=$rel" /etc/apt/sources.list)
echo "$line" | sudo tee /etc/apt/sources.list.d/proposed.list
apt-get update -qq
apt-get install -qy curtin </dev/null
EOF
...
$ lxc exec $name -- dpkg-query --show curtin </dev/null
curtin 0.1.0~bzr470-0ubuntu1~16.10.1
$ lxc exec $name -- curtin version </dev/null
0.1.0~bzr470-0ubuntu1~16.10.1