Refactor Rakefile.
Refactor server debugging & add tags to debugging.
Remove default_config :port in favor of SSHBase default (also 22).
Add required_config attributes for driver.

The following configuration attributes are required for this driver to
function correctly:

* aws_access_key_id
* aws_secret_access_key
* aws_ssh_key_id
* image_id
Fix tailor warnings.
Improvements to README.md.