Public bug reported:
Use-case: You are just starting with Charm Layers, made some layers
locally (in JUJU_REPOSITORY/layers) referenced them with layer:mylayer
and generate the Charm. COMPOSER_PATH is unset
What I expect: Charm compose throws an error saying "I couldn't find the
layer remotely
Public bug reported:
Use-case: You have a "normal" Charm and you start porting it to
composer. You copy the charm from /trusty/mycharm to /layers/mycharm.
You start splitting the charm in layers and run `charm generate mycharm`
Expected result: You get an error explaining that the Charm
