* Add the ability to generate not only UserData sections, but also reused the
  same basic code to also generate config files for the
  AWS::CloudFormation::Init section.
* Moved and modified the code for ref_user_data to a new common method named
  _gen_res_data
* Added a new ref_user_file method and pointed it and ref_user_data at the new
  common _gen_res_data method