10 new mac laptops were added to the swarming pool in 

https://bugs.chromium.org/p/chromium/issues/detail?id=640705

We are seeing some issues on some benchmark runs with the setup of these bots where we need suid: 

See failing task here: 

https://chromium-swarm.appspot.com/user/task/3213407eb6513c10

Log snippet: 
Traceback (most recent call last):
  RunBenchmark at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/internal/story_runner.py:341
    benchmark.ShouldTearDownStateAfterEachStorySetRun())
  Run at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/internal/story_runner.py:227
    _RunStoryAndProcessErrorIfNeeded(story, results, state, test)
  _RunStoryAndProcessErrorIfNeeded at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/internal/story_runner.py:79
    state.WillRunStory(story)
  traced_function at /b/s/w/ir4EeIjg/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:52
    return func(*args, **kwargs)
  WillRunStory at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/page/shared_page_state.py:226
    self._StartBrowser(page)
  traced_function at /b/s/w/ir4EeIjg/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:52
    return func(*args, **kwargs)
  _StartBrowser at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/page/shared_page_state.py:186
    self._browser = self._possible_browser.Create(self._finder_options)
  Create at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/internal/backends/chrome/desktop_browser_finder.py:68
    browser_backend, self._platform_backend, self._credentials_path)
  __init__ at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/internal/browser/browser.py:52
    self.platform.FlushEntireSystemCache()
  FlushEntireSystemCache at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/core/platform.py:179
    return self._platform_backend.FlushEntireSystemCache()
  FlushEntireSystemCache at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/internal/platform/mac_platform_backend.py:178
    p = self.LaunchApplication('purge', elevate_privilege=mavericks_or_later)
  LaunchApplication at /b/s/w/ir4EeIjg/third_party/catapult/telemetry/telemetry/internal/platform/posix_platform_backend.py:144
    raise Exception(text)
Exception: Telemetry needs to run /usr/sbin/purge with elevated privileges, but the setuid bit is not set and there is no interactive terminal for a prompt. Please ask an administrator to set the setuid bit on this executable and ensure that it is owned by a user with the necessary privileges. Aborting.





Similar to issues seen in the past: 

https://bugs.chromium.org/p/chromium/issues/detail?id=337048
https://bugs.chromium.org/p/chromium/issues/detail?id=341490


Could you please troubleshoot the setup on these new mac laptops?