Comment 4 for bug 1334514

This circumstance occurred by heat-engine down in middle of stack processing.
In this case, stack status stuck "UPDATE_IN_PROGRESS".

But I think it's not serious problem basically.
Because IN_PROGRESS stack can clean up by stack-delete.

However, I reported problem is little bit different.
Stack can't clean up because stack-delete failed forever.
I think, it should be fixed, please see the patch.