[Reviewer: Andy] Generic Clearwater Auto Configuration package, and removal of cw-aio

Andy, please can you review my enhancements on top of Tim's changes (but please don't merge - I'll merge this after Tim merges into master)?

The changes are
* addition of a `clearwater-auto-config-generic` package, which sets up `/etc/clearwater/config` from local IP information - note that it doesn't use `hostname -i` because this sometimes seems to give the localhost IP address
* removal of the `cw-aio` flag from `/etc/clearwater/config` - a corresponding change to chef will follow shortly
* improved formatting of prompt when running on console, not on xterm
* use of default hostname if `public_hostname` is actually an IP address.