refactor: move from io/ioutil to io and os package

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

weed/storage/needle_map_metric_test.go

@@ -1,8 +1,8 @@
 package storage
 
 import (
-	"io/ioutil"
 	"math/rand"
+	"os"
 	"testing"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
@@ -11,7 +11,7 @@ import (
 
 func TestFastLoadingNeedleMapMetrics(t *testing.T) {
 
-	idxFile, _ := ioutil.TempFile("", "tmp.idx")
+	idxFile, _ := os.CreateTemp("", "tmp.idx")
 	nm := NewCompactNeedleMap(idxFile)
 
 	for i := 0; i < 10000; i++ {