Change validate message for test_exceed_max_template_size_fails

The error message changed for Template size validation.
This patch change the validation message to match new parttern.

Change-Id: I981d477c96345e68baa5a3d96c6671ad242dbb63
Depends-On: Iddce0260436042e37eebe2aecb810707e53a4473
Partial-Bug: #1499379
diff --git a/tempest/api/orchestration/stacks/test_limits.py b/tempest/api/orchestration/stacks/test_limits.py
index bb5b89d..8c89a85 100644
--- a/tempest/api/orchestration/stacks/test_limits.py
+++ b/tempest/api/orchestration/stacks/test_limits.py
@@ -37,7 +37,7 @@
   Foo: bar''' % fill
         ex = self.assertRaises(lib_exc.BadRequest, self.create_stack,
                                stack_name, template)
-        self.assertIn('Template exceeds maximum allowed size', str(ex))
+        self.assertIn('exceeds maximum allowed size', str(ex))
 
     @test.idempotent_id('d1b83e73-7cad-4a22-9839-036548c5387c')
     def test_exceed_max_resources_per_stack(self):