Added common Constants file under Cloudcafe project

* Common constants file added to have Messages related constants used in
all projects

Change-Id: I961354a89cb23f00b7557ea0fdbd3bae17f95380

cloudcafe/common/constants.py

@@ -0,0 +1,19 @@
+"""
+Copyright 2013 Rackspace
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+
+class Messages:
+    ASSERT_MSG = "Unexpected {0} value received. Expected: {1}, Received: {2}"