refactor: move from io/ioutil to io and os packages (#5266)

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

[1]: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

pkg/apiserver/config/config_test.go

@@ -18,7 +18,6 @@ package config
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 	"testing"
 	"time"
@@ -206,7 +205,7 @@ func saveTestConfig(t *testing.T, conf *Config) {
 	if err != nil {
 		t.Fatalf("error marshal config. %v", err)
 	}
-	err = ioutil.WriteFile(fmt.Sprintf("%s.yaml", defaultConfigurationName), content, 0640)
+	err = os.WriteFile(fmt.Sprintf("%s.yaml", defaultConfigurationName), content, 0640)
 	if err != nil {
 		t.Fatalf("error write configuration file, %v", err)
 	}