S3AFilesystem.initiateRename() can skip check on dest.parent status if src has same parent

Speedup inferred from debug logs (probably not a regression from HADOOP-15183, more something we'd not noticed).

There's a check in initiateRename() to make sure the parent dir of the dest exists.
If dest.getParent() is src.getParent() (i.e. a same dire rename) or is any other ancestor, we don't need those HEAD/LIST requests.