1000% percent improvement with PE agent installs

This big pull request adds:
- A new pe-simplified-agent.sh install script which retrieves packages from its PE Master. 500% improvement in install speed.
- Policy-based certificate autosigning facilities that enable properly configured masters and agents to connect without user intervention.
- A Puppet class that sets up autosigning on a PE master

See the commit messages for more details.

I'm pretty excited about the improvements, making it really easy to build a large, functioning stack in GCE. I'll submit another PR (later) with module metadata and changelog updates for release. This work may need more polish, especially for FOSS, before release.
See previous comment regarding latest image string.