Logging error: I/O operation on closed file

[vandanavk]

Observing this at the end of a run of pytest tests/tensorflow2. Issue most probably introduced after PR https://github.com/awslabs/sagemaker-debugger/pull/259

--- Logging error ---
Traceback (most recent call last):
  File "/usr/lib/python3.6/logging/__init__.py", line 996, in emit
    stream.write(msg)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/capture.py", line 424, in write
    return self.buffer.write(s.encode(self.encoding, "replace"))
ValueError: I/O operation on closed file
Call stack:
  File "/usr/local/lib/python3.6/dist-packages/smdebug/tensorflow/keras.py", line 695, in _cleanup
    super()._cleanup()
  File "/usr/local/lib/python3.6/dist-packages/smdebug/core/hook.py", line 500, in _cleanup
    self._close_writers()
  File "/usr/local/lib/python3.6/dist-packages/smdebug/tensorflow/base_hook.py", line 349, in _close_writers
    self._write_scalars()
  File "/usr/local/lib/python3.6/dist-packages/smdebug/core/hook.py", line 648, in _write_scalars
    if self._is_not_supported():
  File "/usr/local/lib/python3.6/dist-packages/smdebug/tensorflow/keras.py", line 68, in _is_not_supported
    "Executing in TF2.x eager mode."
Message: 'Executing in TF2.x eager mode.SageMaker Debugger will not be saving gradients'

[Vikas-kum]

@NihalHarish ?