Fix fake_init_exception() to better handle Neutron exceptions

Neutron often declares exceptions by overriding the message attribute
and possibly adding additional information later, like a 'reason' for
the failure, rather than passing the code and message around as
arguments.  We should handle this appropriately and display the correct
message, instead of failing with "TypeError: fake_init_exception()
takes exactly 3 arguments (1 given)"

Change-Id: Ib838704cb9ca968ddfc6e3bfed3af7d0ea08f384
Closes-Bug: #1315035

openstack_dashboard/test/test_data/exceptions.py

@@ -27,9 +27,16 @@ from openstack_dashboard.test.test_data import utils
 def create_stubbed_exception(cls, status_code=500):
     msg = "Expected failure."
 
-    def fake_init_exception(self, code, message, **kwargs):
+    def fake_init_exception(self, code=None, message=None, **kwargs):
         self.code = code
-        self.message = message
+        self.message = message or self.__class__.message
+
+        try:
+            # Neutron sometimes updates the message with additional
+            # information, like a reason.
+            self.message = self.message % kwargs
+        except Exception:
+            pass  # We still have the main error message.
 
     def fake_str(self):
         return str(self.message)