Add rubocop to foreman as a lint checker for the Ruby code. A couple notes:

- To generate the config, use --auto-gen-config which will disable all failing rules and create a TODO list of things to address
- Use https://github.com/eitoball/rubocop-checkstyle_formatter to output XML for Jenkins

Check out our rubocop rake task in Katello for running rubocop via Jenkins:

https://github.com/Katello/katello/blob/628a01ad914e7c5d63c8d325e4798a8c19755cff/lib/katello/tasks/rubocop.rake