add missing wait groups for certain io.Pipe() usage (#12264)

wait groups are necessary with io.Pipes() to avoid
races when a blocking function may not be expected
and a Write() -> Close() before Read() races on each
other. We should avoid such situations..

Co-authored-by: Klaus Post <klauspost@gmail.com>

cmd/storage-rest-client.go

@@ -208,11 +208,10 @@ func (client *storageRESTClient) NSScanner(ctx context.Context, cache dataUsageC
 	}()
 	respBody, err := client.call(ctx, storageRESTMethodNSScanner, url.Values{}, pr, -1)
 	defer xhttp.DrainBody(respBody)
+	pr.CloseWithError(err)
 	if err != nil {
-		pr.Close()
 		return cache, err
 	}
-	pr.Close()
 
 	var newCache dataUsageCache
 	pr, pw = io.Pipe()