Delete db resources not in template

When migrating stacks to convergence, if there are resources in
the database that are not in the current_template_id of the stack,
they are possibly of no isue, so it would better to delete those
resources from db to avoid any future update issues.

Change-Id: Ica99cec6765d22d7ee2262e2d402b2e98cb5bd5e
Story: #2004071
Task: 27092

heat/engine/stack.py

@@ -2242,7 +2242,16 @@ class Stack(collections.Mapping):
         db_rsrcs = self.db_active_resources_get()
         if db_rsrcs is not None:
             for res in db_rsrcs.values():
-                res.update_and_save(values=values)
+                # delete db resources not in current_template_id
+                try:
+                    self.defn.resource_definition(res.name)
+                except KeyError:
+                    LOG.warning("Resource %(res)s not found in template "
+                                "for stack %(st)s, deleting from db.",
+                                {'res': res.name, 'st': self.id})
+                    resource_objects.Resource.delete(self.context, res.id)
+                else:
+                    res.update_and_save(values=values)
         self.set_resource_deps()
         self.current_traversal = uuidutils.generate_uuid()
         self.convergence = True