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>

integration/common.go

@@ -18,7 +18,7 @@ package integration
 
 import (
 	"fmt"
-	"io/ioutil"
+	"os"
 	"testing"
 
 	cri "github.com/containerd/containerd/integration/cri-api/pkg/apis"
@@ -56,7 +56,7 @@ func initImages(imageListFile string) {
 	}
 
 	if imageListFile != "" {
-		fileContent, err := ioutil.ReadFile(imageListFile)
+		fileContent, err := os.ReadFile(imageListFile)
 		if err != nil {
 			panic(fmt.Errorf("Error reading '%v' file contents: %v", imageList, err))
 		}