fs: Migrate object metadata to objects directory. (#4195)

Fixes #3352

cmd/posix-list-dir-others.go

@@ -32,6 +32,8 @@ func readDir(dirPath string) (entries []string, err error) {
 		// File is really not found.
 		if os.IsNotExist(err) {
 			return nil, errFileNotFound
+		} else if os.IsPermission(err) {
+			return nil, errFileAccessDenied
 		}
 
 		// File path cannot be verified since one of the parents is a file.