Fix colorizier thowing exception when a test fails

This failure in colorizier was hidding the actual error
in the tests. If we ran enough tests it also became difficult
to see which test had actually failed.

Fixes: bug 1183602

Change-Id: I806da8f13040b38258de7f3e0fa7b62700bdcead

tools/colorizer.py

@@ -232,6 +232,8 @@ class NovaTestResult(testtools.TestResult):
         self._addResult(test, 'OK', 'green', '.', True)
 
     def addFailure(self, test, err):
+        if test.id() == 'process-returncode':
+            return
         super(NovaTestResult, self).addFailure(test, err)
         self._addResult(test, 'FAIL', 'red', 'F', False)