forj-docker supports creating erb based Docker file for nodes

* add erb_data class for processing erb data
* each node will have a repo_name/blueprint:node_name
* manage edits to the Rakefile if one exist otherwise
  install a sample Rakefile
* install a vagrantfile

Change-Id: Ic6f8b48d6155f37d56e0a6f34ad80853096fff94