Comment 12 for bug 1423980

This seems to be related to the fact that, in the provided bundles, some service have unit placements pointing to a subordinate charm. Perhaps I am missing something, but this should not be allowed: since IIRC subordinates don't have units, pointing to them for unit placement does not make much sense.
For instance, the calico.yaml bundle has neutron-api placed to lxc:neutron-calico=0, the latter being a subordinate.

What's the expected deployer behavior in such cases? I assumed an error should be returned, but, as I said, I can be wrong.
Of course the error here is not helpful, so I attached a branch that improves unit placement validation, so that the bundle deployment fails sooner rather than later and with a more meaningful error, e.g.:
Cannot place to a subordinate service: neutron-api -> neutron-calico