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/endpoint_test.go

@@ -6,7 +6,6 @@
 package virtcontainers
 
 import (
-	"io/ioutil"
 	"net"
 	"os"
 	"reflect"
@@ -87,7 +86,7 @@ func TestIncorrectEndpointTypeString(t *testing.T) {
 func TestSaveLoadIfPair(t *testing.T) {
 	macAddr := net.HardwareAddr{0x02, 0x00, 0xCA, 0xFE, 0x00, 0x04}
 
-	tmpfile, err := ioutil.TempFile("", "vc-Save-Load-net-")
+	tmpfile, err := os.CreateTemp("", "vc-Save-Load-net-")
 	assert.Nil(t, err)
 	defer os.Remove(tmpfile.Name())