mumble-server charm

HI Kees! Thanks for another charm. Review here:

=== Blocking Issues ===

* The default password of 'unset' is not checked for in config-changed. This hook is always called once right after the charm gets to a 'started' state, so if the user forgets to set the password, they will have a mumble server with the password of 'unset'. We've decided to disallow charms which set default passwords. I'd recommend checking for it, and just exitting config-changed quietly if it is still 'unset'.

* The interface name of 'settings' seems *really* generic. The idea is to keep people from accidentally relating incompatible services together. I'm not sure settings will do enough to prevent that, and it may produce some confusion.

Can it just be 'interface: mumble' instead and drop the protocol bit?

* hostname -f is not reliable enough, as some providers will set things up in a way where hostname -f returns a bogus address. use `unit-get private-address` instead. The private address is always the one that will (should!) be accessible from other nodes in the same environment.

==== Next Steps ====

If you can address those, we can promulgate this into the store. It should be a nice addition. :)

Thanks for the feedback! I've cleaned up the issues you mentioned and expanded the scope of the service. Now it will auto-generate trees of Mumble channels based on the services (and service units) that start relationships with the mumber-server.

Please consider this submission for the Juju Charm Contest at UDS. (See you there!)

IIUC, this is the first charm for the store to actually define a "juju-info" relationship so that arbitrary services can be trivially bound to the mumble-server service, there by making the "Integration with other services" limitless. :)

Nice job on the fixes Kees. Tested, works great, and really thats a very cool idea. I'm not sure I see the full utility of a "channel per unit" but the very existence of the relationship is interesting enough to want to explore that more. It is, I think, the first charm in the store that requires a non-container-scoped juju-info, yes. :)

Promulgated and available now as lp:charms/mumble-server (and should be in the store soon, available to deploy as just 'juju deploy mumble-server'.