Code review comment for ~hloeung/charm-telegraf:master

@hloeung Your proposal would not work as what you expect. Juju uses the `runs-on` definitions in charmcraft.yaml to decided whether a revision can be deployed on a Ubuntu series. So without adding xenial support in charmcraft.yaml, the charm built on top of your changes will not be recognized as a revision that xenial telegraf deployment can be upgraded to.

I agree with Robert, an internal discussion is needed to determine whether supporting a more-complicated release workflow is possible/desirable.