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

tools/colorizer.py

@@ -304,8 +304,12 @@ class NovaTestResult(testtools.TestResult):
 
 
 test = subunit.ProtocolTestCase(sys.stdin, passthrough=None)
-runner = unittest.TextTestRunner(verbosity=2,
-                                 resultclass=NovaTestResult)
+
+if sys.version_info <= (2, 6):
+    runner = unittest.TextTestRunner(verbosity=2)
+else:
+    runner = unittest.TextTestRunner(verbosity=2, resultclass=NovaTestResult)
+
 if runner.run(test).wasSuccessful():
     exit_code = 0
 else: