Code review comment for lp:~negronjl/pyjuju/874801

Re: bug report discussion: this is clear and simple; it seems to be genuinely useful to some potential users; it doesn't add any real complexity to juju as it stands. My only worry is that it may be somewhat tedious to maintain (or just become useless) when we allow co-located units, and by including it we are setting up an expectation that it will continue to work; this makes me personally -0 on the proposal, but other people seem to like it a lot so I'm comfortable approving it nonetheless.