Add a better error message

This was "ERROR" in the event status description.

Change-Id: I401bbbe1c8e8cafe64a692b7faba63bd2ab38a4c
Signed-off-by: Angus Salkeld <asalkeld@redhat.com>

heat/engine/instance.py

@@ -265,7 +265,9 @@ class Instance(Resource):
                 self.ipaddress = server.networks[n][0]
                 break
         else:
-            raise exception.Error(server.status)
+            raise exception.Error('%s instance[%s] status[%s]' %
+                                  ('nova reported unexpected',
+                                   self.name, server.status))
 
     def validate(self):
         '''