Fix test_multithreading on Python 3

* On Python 3, the printer doesn't encode Unicode to utf8 anymore, since
  print() expects a Unicode string.

* Update unit tests for Python 3 since repr() doesn't escape non-ASCII
  characters in Unicode strings anymore:
  http://legacy.python.org/dev/peps/pep-3138/

Change-Id: I89471019d691a46651312d6a49964b719192148a
Merge "Fix test_multithreading on Python 3"