fix post stop hook not always called successfully

[abel-von]

If the first time post stop hook called with a failure(maybe because some resources is not ready to be recycled), the second retry of runc delete will return directly because the container root directoy is already removed. so that the post stop hook is not called.

I think we may have to do container root dir removal after post stop hook executed. I think it is also more consistant with the sematics of "Poststop", because otherwise it should be "PostDelete".

fix #4363