py2.6 doesn't support TextTestRunner resultclass

Updates tools/colorizer to account for the fact that Python
2.6 doesn't support resultclass.

This fixes issue in trying to use run_tests.sh on distributions
which use python 2.6.

Fixes LP Bug #1158940

Change-Id: I763cd9c7a4b5ec5baaad3a3d9ee96e6e3cd13b3e