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>

storage/kubernetes/client_test.go

@@ -3,7 +3,6 @@ package kubernetes
 import (
 	"hash"
 	"hash/fnv"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -72,7 +71,7 @@ func TestInClusterTransport(t *testing.T) {
 	fpath := filepath.Join(os.TempDir(), "test.in_cluster")
 	defer os.RemoveAll(fpath)
 
-	err = ioutil.WriteFile(fpath, []byte("def"), 0o644)
+	err = os.WriteFile(fpath, []byte("def"), 0o644)
 	require.NoError(t, err)
 
 	tests := []struct {
@@ -136,7 +135,7 @@ func TestGetClusterConfigNamespace(t *testing.T) {
 
 	var namespaceFile string
 	{
-		tmpfile, err := ioutil.TempFile(os.TempDir(), "test-get-cluster-config-namespace")
+		tmpfile, err := os.CreateTemp(os.TempDir(), "test-get-cluster-config-namespace")
 		require.NoError(t, err)
 
 		_, err = tmpfile.Write([]byte("namespace-from-file"))