Fixed up a missing space in an error message

Change-Id: Id975b336c8cf139af021ebbbfe398313e31b8881
diff --git a/tempest/test.py b/tempest/test.py
index 7787790..68cedf0 100644
--- a/tempest/test.py
+++ b/tempest/test.py
@@ -97,7 +97,7 @@
 
 def validate_tearDownClass():
     if at_exit_set:
-        raise RuntimeError("tearDownClass does not calls the super's"
+        raise RuntimeError("tearDownClass does not calls the super's "
                            "tearDownClass in these classes: "
                            + str(at_exit_set))