code: def repo_in_defined_envs(repo, all_envs):
      
      remaining_envs = set(repo['env']) - set(all_envs)
      if set(repo['env']) - set(all_envs):
          raise JuicerRepoInUndefinedEnvs("Repo def %s references undefined environments: %s" %
                                          (repo['name'], ", ".join(list(remaining_envs))))
      else:
          return True
docs: Raises exception if the repo references undefined environments