code: def _build_cmdline(self, args, env={}):
          
          if self._user is None:
              return super(RunExecutor, self)._build_cmdline(args, env)
          result = _SUDO_ARGS + [self._user]
          for var, value in env.items():
              result.append(var + '=' + value)
          return result + ['--'] + args
docs: Build the final command line for executing the given command,
          using sudo if necessary.