Fix typo in base.py

There is a typo in SetUpClass in base.py, this typo
hinders running integration tests for client.

Change-Id: I50fba55025729737f4850c4687dac9093dcf235f

functionaltests/base.py

@@ -30,7 +30,7 @@ class MistralBase(testtools.TestCase):
         cls.definition = open(os.path.join(
             __location, 'hello.yaml'), 'rb').read()
 
-        cls.wb = cls.mistral_client_workbooks.create(
+        cls.wb = cls.mistral_client.workbooks.create(
             "wb", "Description", ["tags"])
 
     @classmethod