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.
I try to get in the habit of updating these image strings so they're current as of the latest update.  We're now using, centos-6-v20140718.