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

I think you misunderstood my point. Yes, charmcraft is the tool building the charm, but my point is the way Juju determines whether a revision of the charm can support a specific series is to call a charmhub API which contains the series information defined under `runs-on` in charm's `charmcraft.yaml`. So your proposal, pinging python packages to lower versions without explicitly adding xenial support in charmcraft.yaml, won't work because when juju queries charmhub, it sees that this new revision based on your changes is not xenial-compatible, even if the code itself and the python packages packed inside it are.