Documentation update, new config settings

- Some documentation clarification. I got bit by the expectation of a particular file in .ssh (I have multiple keys, but none are named using the default).

- Add two new configuration options, RE: TCP checks to detect if SSH is ready (these make all kinds of bad assumptions, so allow us to turn them off). test-kitchen currently has 34 pull requests, so I'm not optimistic this will be solved there any time soon.

(see full commit messages for each item, as I described each in detail)