More fixes for our use-case of this plugin

ssh-agent not being disabled by the mcollective daemon made things look like they were working (with 1 node), but they weren't - I've turned this off universally (in the server side verifier) as using the user's agent in the server is just bad news.

Subsequent to this, I needed to change the config to our custom authorized_keys path, which isn't /home/%u/.ssh/authorized_keys - so I made %u interpolate in the same way you can use it in an ssh config.