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>

snapshots/storage/metastore_test.go

@@ -19,7 +19,6 @@ package storage
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"testing"
 	"time"
@@ -67,7 +66,7 @@ func MetaStoreSuite(t *testing.T, name string, meta func(root string) (*MetaStor
 func makeTest(t *testing.T, name string, metaFn metaFactory, fn testFunc) func(t *testing.T) {
 	return func(t *testing.T) {
 		ctx := context.Background()
-		tmpDir, err := ioutil.TempDir("", "metastore-test-"+name+"-")
+		tmpDir, err := os.MkdirTemp("", "metastore-test-"+name+"-")
 		if err != nil {
 			t.Fatal(err)
 		}