Remove unconditional return of user_id

This removes a legacy backwards compatibility codepath. Pre-Icehouse
stacks that have resources which inherit from StackUser may require
manual cleanup after deletion, as their stack user may not be deleted.

This fixes issues with subusers using software config. Heat should not
attempt to delete the stack user if one had not been created before.
The code that this patch removes caused an ID to always be returned.
Additionally, it set the ID in the resource metadata whether a stack
user existed or not, making it impossible to tell if one existed only
from data within the resource.

Change-Id: I50804998fdce1f7de06906ae9a2f47317721a6f6
Closes-bug: #1531606

heat/engine/resources/stack_user.py

@@ -72,15 +72,6 @@ class StackUser(resource.Resource):
         user_id = self.data().get('user_id')
         if user_id:
             return user_id
-        else:
-            # FIXME(shardy): This is a legacy hack for backwards compatibility
-            # remove after an appropriate transitional period...
-            # Assume this is a resource that was created with
-            # a previous version of heat and that the resource_id
-            # is the user_id
-            if self.resource_id:
-                self.data_set('user_id', self.resource_id)
-                return self.resource_id
 
     def handle_delete(self):
         self._delete_user()

releasenotes/notes/legacy-stack-user-id-cebbad8b0f2ed490.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - If upgrading with pre-icehouse stacks which contain resources that create
+    users (such as OS::Nova::Server, OS::Heat::SoftwareDeployment, and
+    OS::Heat::WaitConditionHandle), it is possible that the users will not be
+    removed upon stack deletion due to the removal of a legacy fallback code
+    path. In such a situation, these users will require manual removal.