Adds error_code in heat exceptions

Tags a given exception with error code. It helps
to report or handle the exception based the code.

implements blueprint: heat-template-validate-improvements

Change-Id: Iea6599c1602e57ce4020303e56c839d1a6a8ac52

heat/common/exception.py

@@ -55,12 +55,16 @@ class HeatException(Exception):
     provided to the constructor.
     """
     message = _("An unknown exception occurred.")
+    error_code = None
 
     def __init__(self, **kwargs):
         self.kwargs = kwargs
 
         try:
             self.message = self.msg_fmt % kwargs
+
+            if self.error_code:
+                self.message = 'HEAT-E%s %s' % (self.error_code, self.message)
         except KeyError:
             exc_info = sys.exc_info()
             # kwargs doesn't match a variable in the message

heat/tests/test_common_exception.py

@@ -0,0 +1,34 @@
+#
+#    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.
+
+from heat.common import exception
+from heat.tests import common
+
+
+class TestException(common.HeatTestCase):
+
+    class SampleExceptionNoErorCode(exception.HeatException):
+        msg_fmt = 'Test exception'
+
+    class SampleException(SampleExceptionNoErorCode):
+        error_code = 100
+
+    def test_heat_exception_no_error_code(self):
+        ex = TestException.SampleExceptionNoErorCode()
+        self.assertEqual('Test exception',
+                         ex.message)
+
+    def test_heat_exception_with_error_code(self):
+        ex = TestException.SampleException()
+        self.assertEqual('HEAT-E100 Test exception',
+                         ex.message)