For some time there have been cloud-init daily builds at
https://code.launchpad.net/~cloud-init-dev/+recipe/cloud-init-daily

That was building upstream/master with the upstream/devel packaging branch
and publishing for zesty, yakkety, and xenial.

But for some time, the upstream ubuntu/xenial and ubuntu/yakkety have had
different packaging than the upstream/devel.  That was because they had
small patches to change behavior of cloud-init for SRU reasons.

To my knowledge, the recipe building system cannot build for each release
from a different branch, so for now I have 3 recipes instead of 1.
  https://code.launchpad.net/~cloud-init-dev/+recipe/cloud-init-daily-xenial
  https://code.launchpad.net/~cloud-init-dev/+recipe/cloud-init-daily-yakkety
  https://code.launchpad.net/~cloud-init-dev/+recipe/cloud-init-daily-devel

The recipe looks like:
  # git-build-recipe format 0.4 deb-version {latest-tag}-{revno}-g{git-commit}-0ubuntu1+{revno:ubuntu-pkg}~trunk
  lp:cloud-init master
  merge ubuntu-pkg lp:cloud-init ubuntu/devel

They differ only in the 'devel' -> [xenial | yakkety]

I don't love the solution, but I think it ends up working best, outside of
having support in the recipe to substitute 'devel'.

I'm seeing upload errors at
 https://code.launchpad.net/~cloud-init-dev/+recipe/cloud-init-daily-xenial
 https://code.launchpad.net/~cloud-init-dev/+recipe/cloud-init-daily-yakkety