Support Python 2 and 3 in test script

Add Python 3 support to the Python test.py script.

The print function is used in place of the print statement.

The urlopen function has been moved to urllib.request in Python 3, so
attempt to import it from either location.

TestCase.assert_() has been deprecated in place of
TestCase.assertTrue().

The tests all pass in both Python 2 and 3.