Add test for updateUploadJSON (Fixes #3060) (#3155)

cmd/xl-v1-multipart-common.go

@@ -54,7 +54,7 @@ func (xl xlObjects) updateUploadJSON(bucket, object string, uCh uploadIDChange)
 			// If we have a read error, we store error and
 			// exit.
 			if err != nil {
-				errs[index] = traceError(err)
+				errs[index] = err
 				return
 			}