Comment 4 for bug 1625766

This code path is involved on each boot, but on Ubuntu we never triggered the failure case. Failure case happens when some drivers were in different state. I realize this is not great, but I'm marking this as verification-done based on:

$ release=yakkety
$ lxc launch "ubuntu-daily:$release" "$name"
$ lxc exec $name -- dpkg-query --show cloud-init
cloud-init 0.7.8-49-g9e904bb-0ubuntu1~16.10.1

$ lxc file pull $name/etc/cloud/build.info -
build_name: server
serial: 20170119

## enable proposed, update
$ m=http://archive.ubuntu.com/ubuntu;
$ echo "deb $m $release-proposed main" | lxc file push - $name/etc/apt/sources.list.d/proposed.list
$ lxc exec $name -- sh -c 'apt update -q && apt install cloud-init' </dev/null
$ lxc exec $name -- dpkg-query --show cloud-init
cloud-init 0.7.8-68-gca3ae67-0ubuntu1~16.10.1

# clean up to make it look like first boot.
$ lxc exec $name -- sh -c 'cd /var/lib/cloud; for d in *; do [ "$d" = "seed" ] || rm -vRf "$d"; done'
$ lxc exec $name -- sh -c 'rm -f /var/log/cloud*'
$ lxc restart $name

$ lxc exec $name -- grep WARN /var/log/cloud-init.log || echo no warn
no warn

$ lxc lau