configuring a ubuntu 12.04 compatible rbenv

The recipe tries to use LWRPs -- and it might actually work, the original problem is the current_user is not properly interpreted from the default.yml in Kitchenplan.

However, this is my tested and working method to install rbenv.  I am not sure why node['current_user'] is not correctly looked up, but the code fails trying to find 'current_user' -> perhaps this is a string interp problem? Regardless the recipe below workson Ubuntu Desktop 12.04 LTS.