Added the ability override config values in knife.rb from Vagrantfile
Validate knife config file exists if specified
Added comment for plugin section
Added encrypted_data_bag_secret mapping
Bootstrap log4r plugin logging
Extracted core plugin logic to ChefClientConfigurator class

Refactored configuration setting to only override values that are unset in the Vagrantfile. Added log4r debug level logging so users can tell what's going on - where are their values for their chef client provisioners coming from and what are they being set too