peach_pit-tot-chrome-pfq-informational failed in http://cros-goldeneye/chromeos/healthmonitoring/buildDetails?buildbucketId=8942067206169611824 during the CleanUp stage while trying to remove the chroot.

Congbin (or others), any ideas about what went wrong here? I'm not sure whether we collect any information from the builder that would help determine why the command was hanging for four minutes.

...
17:31:57: INFO: Cleaning up buildroot git repositories.
17:31:57: INFO: Resetting all repo branches: /b/swarming/w/ir/cache/cbuild/repository
17:31:57: INFO: Wiping old output.
17:31:57: INFO: Deleting archived trybot images.
17:31:57: INFO: Deleting archived perf results.
17:31:57: INFO: Deleting autotest site packages.
17:31:57: INFO: Deleting Chrome build output.
17:31:57: INFO: Deleting chroot.
17:35:59: ERROR: <class 'chromite.lib.timeout_util.TimeoutError'>: Timeout occurred- waited 240.0 seconds.
Traceback (most recent call last):
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/parallel.py", line 442, in _Run
    self._task(*self._task_args, **self._task_kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/stages/build_stages.py", line 96, in _DeleteChroot
    cros_sdk_lib.CleanupChrootMount(chroot, delete=True)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/timeout_util.py", line 191, in TimeoutWrapper
    return func(*args, **kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/cros_sdk_lib.py", line 412, in CleanupChrootMount
    osutils.RmDir(chroot, ignore_missing=True, sudo=True)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/osutils.py", line 357, in RmDir
    redirect_stdout=True, redirect_stderr=True)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/cros_build_lib.py", line 325, in SudoRunCommand
    return RunCommand(sudo_cmd, **kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/cros_build_lib.py", line 637, in RunCommand
    (cmd_result.output, cmd_result.error) = proc.communicate(input)
  File "/usr/lib/python2.7/subprocess.py", line 796, in communicate
    self.wait()
  File "/usr/lib/python2.7/subprocess.py", line 1376, in wait
    pid, sts = _eintr_retry_call(os.waitpid, self.pid, 0)
  File "/usr/lib/python2.7/subprocess.py", line 476, in _eintr_retry_call
    return func(*args)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/timeout_util.py", line 88, in kill_us
    raise TimeoutError(error_message % {'time': max_run_time})
TimeoutError: Timeout occurred- waited 240.0 seconds.