stack is in a wrong state

[huangtianhua]

1. create a stack with a heat autoscaling group
2. update the stack to change the size of the group manually, and rollback=true
3. something wrong when group scale, so nested stack enter rollback flow
4. the nested stack rollback successful, but the top stack is in UPDATE_FAILED

We set nested stack to UPDATE_FAILED before the nested stack entering rollback, and meanwhile the group check whether the nested stack update complete, and happened the UPDATE_FAILED.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/470080

[Zane Bitter (zaneb)]

Was this in a legacy stack or convergence?

Nested stacks should never rollback:

http://git.openstack.org/cgit/openstack/heat/tree/heat/engine/resources/stack_resource.py#n215

so it's strange that this one is.