juju-* relations are reserved

Several charms have relations named "juju-*", which are disallowed in go (and inappropriate in python, anyway -- there's an implicit "juju-info" relation that *every* charm provides, and we can't have duplicate relation names).

`charm proof` should be fixed to warn about this (if not error immmediately); and any charms using juju-* relations should be fixed.

For reference, the restrictions are as follows:

1) no relation can be named "juju" or "juju-*"
2) no file in the hooks directory can be named "juju" or "juju-*"
3) no relation can *provide" an interface named "juju" or "juju-*"

(note that of course it is valid for a relation to *require* a "juju-*" interface, otherwise nothing can use the implicit "juju-*" interfaced relations)