Minor clean ups from model unification.
Minor clean ups from model unification.

* XXX notes have been consolidated to indicate what should actually be done once
possible.
* The checks in BrowserCharm.parse have been updated based on investigation into
the PyJuju and GoJuju environments. As the data passed is consistently in one
form or another, we now just check if "config" exists and parse
the data as needed in that case.

R=matthew.scott, rharding
CC=
https://codereview.appspot.com/12897043

bac/juju-gui,mitechie/juju-gui,jrwren/juju-gui,CanonicalJS/juju-gui,jrwren/juju-gui,bac/juju-gui,jrwren/juju-gui,mitechie/juju-gui,mitechie/juju-gui,CanonicalJS/juju-gui,jrwren/juju-gui,bac/juju-gui,bac/juju-gui,mitechie/juju-gui,CanonicalJS/juju-gui