test: fix unit test logging with python3

A logfile must be opened as a text file and encoding is specified.
Then it can accept a string. Current behaviour we get,

 Message: 'ok 2834 sequential/test-worker-prof'
 Arguments: ()
 --- Logging error ---
 Traceback (most recent call last):
   File "/usr/lib64/python3.7/logging/__init__.py", line 1037, in emit
     stream.write(msg + self.terminator)
 TypeError: a bytes-like object is required, not 'str'
 Call stack:
   File "tools/test.py", line 1734, in <module>
     sys.exit(Main())
   File "tools/test.py", line 1710, in Main
     if RunTestCases(cases_to_run, options.progress, options.j, options.flaky_tests):
   File "tools/test.py", line 933, in RunTestCases
     return progress.Run(tasks)
   File "tools/test.py", line 141, in Run
     self.RunSingle(False, 0)
   File "tools/test.py", line 202, in RunSingle
     self.HasRun(output)
   File "tools/test.py", line 365, in HasRun
     logger.info('  ---')

PR-URL: https://github.com/nodejs/node/pull/31156


Reviewed-By: Christian Clauss <cclauss@me.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>