convergence: resources not using the correct template on update

[Angus Salkeld]

If you make a trivial template and update it, you will notice that the new changes will not happen (even tho' it says Update complete).

From what I have figured out:

1. stack.prev_raw_template_id is set straight away
https://github.com/openstack/heat/blob/master/heat/engine/stack.py#L943-L944

2. The old resource is "found" by matching it's previous template id to the above
https://github.com/openstack/heat/blob/master/heat/engine/stack.py#L1011

New resource instances are not made for the new template. If we had resource ZZ in the old
template
ZZ:
  properties:
     foo: 5

and in the new template:
ZZ:
  properties:
     foo: 6

I was expecting an new resource instance with the new template id attached.

[Angus Salkeld (asalkeld)]

https://review.openstack.org/#/c/193936/

[Zane Bitter (zaneb)]

https://review.openstack.org/#/c/193936/ merged, so changing to Fix Committed.