PROTON-2319: A (hopefully) final piece of python 2.6 detritus

 Please enter the commit message for your changes. Lines startin
diff --git a/python/tests/proton_tests/common.py b/python/tests/proton_tests/common.py
index a56a2c0..89d90bd 100644
--- a/python/tests/proton_tests/common.py
+++ b/python/tests/proton_tests/common.py
@@ -20,14 +20,7 @@
 from __future__ import absolute_import
 
 from unittest import TestCase
-try:
-  from unittest import SkipTest
-except:
-  try:
-    from unittest2 import SkipTest
-  except:
-    class SkipTest(Exception):
-      pass
+from unittest import SkipTest
 
 import sys, os, subprocess
 from random import randint