Fails test under python 3.6

Under Python 3.6, there's the below issue with unit tests when building the Debian package. Note that for me, it worked in Python 2.7 and 3.5.

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FAIL: proliantutils.tests.ilo.test_firmware_controller.FirmwareImageExtractorTestCase.test_successive_calls_to_extract_method
proliantutils.tests.ilo.test_firmware_controller.FirmwareImageExtractorTestCase.test_successive_calls_to_extract_method
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_StringException: Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/mock/mock.py", line 1305, in patched
    return func(*args, **keywargs)
  File "/home/zigo/sources/openstack/pike/python-proliantutils/build-area/python-proliantutils-2.4.1/proliantutils/tests/ilo/test_firmware_controller.py", line 473, in test_successive_calls_to_extract_method
    raw_fw_file, is_extracted = fw_img_extractor.extract()
  File "/home/zigo/sources/openstack/pike/python-proliantutils/build-area/python-proliantutils-2.4.1/proliantutils/ilo/firmware_controller.py", line 273, in extract
    extract_path = os.path.join(temp_dir, self.fw_filename)
  File "/usr/lib/python3.6/posixpath.py", line 78, in join
    a = os.fspath(a)
TypeError: expected str, bytes or os.PathLike object, not MagicMock