Fix log_invocation function to pass unittests on python3

Normalize this function to use native strings.  Native strings won't
display an extra "u" or "b" character to denote py2 unicode or py3 bytes
types.

test/units/module_utils/basic/test__log_invocation.py

@@ -30,7 +30,6 @@ from ansible.compat.tests.mock import MagicMock
 
 
 class TestModuleUtilsBasic(unittest.TestCase):
-    @unittest.skipIf(sys.version_info[0] >= 3, "Python 3 is not supported on targets (yet)")
     def test_module_utils_basic__log_invocation(self):
         with swap_stdin_and_argv(stdin_data=json.dumps(
             dict(