heat engine : Update stack dependencies during update

heat engine : Update stack dependencies during update

We need to update the stack dependencies each time we modify the
resources list, otherwise in the event of a failure, the resources
returned from the iterator methods don't match with those found via
getitem/contains (which is important for rollback)

blueprint update-rollback

Change-Id: Ia47f84291f50c33fc052b7b33fa0c1f9e8430ab4