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.
In the old rakefile, I tried to verify that the download was complete using the .asc file for the installer. Would be nice to have that as protection against things failing due to incomplete downloads. As a bonus, you can use it to verify that any existing downloaded file is indeed a complete installer, before downloading the installer again.