runtime: change io/ioutil to io/os packages

Change io/ioutil to io/os packages because io/ioutil package
is deprecated from 1.16:

Discard => io.Discard
NopCloser => io.NopCloser
ReadAll => io.ReadAll
ReadDir => os.ReadDir
ReadFile => os.ReadFile
TempDir => os.MkdirTemp
TempFile => os.CreateTemp
WriteFile => os.WriteFile

Details: https://go.dev/doc/go1.16#ioutil

Fixes: #3265

Signed-off-by: bin <bin@hyper.sh>

src/runtime/virtcontainers/mount_test.go

@@ -9,7 +9,6 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -241,7 +240,7 @@ func TestIsEphemeralStorage(t *testing.T) {
 		t.Skip(ktu.TestDisabledNeedRoot)
 	}
 
-	dir, err := ioutil.TempDir(testDir, "foo")
+	dir, err := os.MkdirTemp(testDir, "foo")
 	assert.NoError(err)
 	defer os.RemoveAll(dir)
 
@@ -319,7 +318,7 @@ func TestIsWatchable(t *testing.T) {
 	result = isWatchableMount(path)
 	assert.False(result)
 
-	testPath, err := ioutil.TempDir("", "")
+	testPath, err := os.MkdirTemp("", "")
 	assert.NoError(err)
 	defer os.RemoveAll(testPath)