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/sandbox_clean_remove_test.go

@@ -20,7 +20,6 @@
 package integration
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -40,11 +39,11 @@ func TestSandboxRemoveWithoutIPLeakage(t *testing.T) {
 	t.Logf("Make sure host-local ipam is in use")
 	config, err := CRIConfig()
 	require.NoError(t, err)
-	fs, err := ioutil.ReadDir(config.NetworkPluginConfDir)
+	fs, err := os.ReadDir(config.NetworkPluginConfDir)
 	require.NoError(t, err)
 	require.NotEmpty(t, fs)
 	f := filepath.Join(config.NetworkPluginConfDir, fs[0].Name())
-	cniConfig, err := ioutil.ReadFile(f)
+	cniConfig, err := os.ReadFile(f)
 	require.NoError(t, err)
 	if !strings.Contains(string(cniConfig), "host-local") {
 		t.Skip("host-local ipam is not in use")