Changes for automated build process

This looks like more than it really is because of the two new modules.  Mostly it's just refactoring the build process and moving things around.

- Creates a new Rakefile that is used by the automated build process and updates README to reflect new usage.
- Fixes Vagrantfile and uses standard Centos base box
- Fixes gem caching to recognize pre-cached files from Vagrant or other build tools
- Adds local cache for PE & PE Agent downloads and puppetizes staging
- Implements epel module instead RPM based install
- Moves some of packer build scripts from another repo to be used for possible future packer build.
I'm not sure this is the ideal student experience. I think I'd prefer something like:

    Your machine has the following IP addresses: 172.16.144.123, 192.168.0.2
    Please enter the main external address [172.16.144.123]: _

Or:

    This machine has the following IP addresses:

    1: 172.16.144.123
    2: 192.168.0.2

    Please choose your main external IP [1]:_

I suppose the simplest option might be:

    This machine has the following IP addresses:

    1: 172.16.144.123
    2: 192.168.0.2

    Is the main external IP address 172.16.144.123 [Y/n]? n
    Is the main external IP address 192.168.0.2 [Y/n]?