A slight improvement to #2399 - if bind is localhost, return an error
instead of advertising a private ip. The advertised ip isn't valid and
will just cause errors on use. It's better to fail with an error message
instructing users how to fix the problem.
I apologize in advance for the rather long PR, but unfortunately there
is not an easy way to break this up into smaller chunks. This separates
the agent configuration into smaller, more consumable pieces just like
the job specification.
