User-specific stuff in config files

[tvoran]

Might be better to have the ability to set user-specific things like ssh private keys with environment variables in the .conf files (like access_id and secret_key are in clouds.conf).

i.e.

[DEFAULT]
key_name = automaton
key_path = $SSH_PUBLIC_KEY

instead of

[DEFAULT]
key_name = automaton
key_path = /home/user/.ssh/id_rsa.pub

The end goal is to keep user-specific stuff out of the repository, so maybe it's easier to just mark the conf files in the repo as examples, and force the user to create their own .conf files.