Change rubocop rake task to not return an exit error on failure
Change rubocop rake task to not return an exit error on failure

* At the moment rubocop does not allow granular enough configuration
  to override a specific setting on a per-file or per-class basis.
  This will be required before we can fail the build when there are
  offences identified by rubocop.

mvz/devtools,zaidan/devtools,sferik/devtools,backus/devtools,mbj/devtools,JonathonMA/devtools