run-tests: implement Test.__str__

unittest sometimes does a str(test) and the default implementation
doesn't do the right thing. So we override it.

tests/run-tests.py

@@ -387,6 +387,9 b' class Test(object):'
             # will try again.
             shutil.rmtree(self._threadtmp, True)
 
+    def __str__(self):
+        return self.name
+
     def setUp(self):
         """Tasks to perform before run()."""
         self._finished = False