Comment 1 for bug 1618155

The problem is caused due to commit 084d0eb20f6636b63721eb3c5a9db08858d05ec5 where we update the current traversal in state_set, and by doing so we loose the previous traversal. Since we loose the previous traversal ID, there is no way to go back and delete it. The code at https://github.com/openstack/heat/blob/master/heat/engine/check_resource.py#L75 is causing the issue.

My worry is that we do state_set at various places and implicitly setting the current traversal is not a good idea. The solution is to probably just update the current traversal as another instruction/method so that we know what action needs to be taken explicitly when we do so.