Working user-data script

This can either go into your image on the cloud-init
directory /var/lib/cloud/instance/scripts, or you can
add it to user-data on the instance creation.
Updated README with talk, added master config to enable $trusted

The drawings and walkthrough came from my puppetconf talk
Had to enable the trusted hash since it's not necessarily on by default.
Updates to autosign.rb

Use ruby from the environment, not necessarily /opt/puppet/bin
Adds a PSK check and move it to the top to avoid hitting the
  network unnecessarily
Add an image name extension, just for good luck