tests/unit/test_config.py fails

[Isaku Yamahata]

tests/unit/test_config.py fails when extra options are passed to run_tests.py

  The first test in test_config.TestConfig.test_parse_options tests
  no options are specified. But it checks sys.argv when default parameter
  is used. So it fails when some parameter is passed to run_test.py.
  So pass empty list to the parser as argument explicitly in order to
  make it pass independent sys.argv.