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>

cmd/containerd/command/main.go

@@ -19,7 +19,7 @@ package command
 import (
 	gocontext "context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net"
 	"os"
 	"os/signal"
@@ -56,7 +56,7 @@ high performance container runtime
 
 func init() {
 	// Discard grpc logs so that they don't mess with our stdio
-	grpclog.SetLoggerV2(grpclog.NewLoggerV2(ioutil.Discard, ioutil.Discard, ioutil.Discard))
+	grpclog.SetLoggerV2(grpclog.NewLoggerV2(io.Discard, io.Discard, io.Discard))
 
 	cli.VersionPrinter = func(c *cli.Context) {
 		fmt.Println(c.App.Name, version.Package, c.App.Version, version.Revision)

cmd/containerd/command/publish.go

@@ -19,7 +19,6 @@ package command
 import (
 	gocontext "context"
 	"io"
-	"io/ioutil"
 	"net"
 	"os"
 	"time"
@@ -73,7 +72,7 @@ var publishCommand = cli.Command{
 }
 
 func getEventPayload(r io.Reader) (*types.Any, error) {
-	data, err := ioutil.ReadAll(r)
+	data, err := io.ReadAll(r)
 	if err != nil {
 		return nil, err
 	}

cmd/containerd/command/service_windows.go

@@ -18,7 +18,7 @@ package command
 
 import (
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"os"
 	"path/filepath"
@@ -249,7 +249,7 @@ func registerUnregisterService(root string) (bool, error) {
 			return true, err
 		}
 
-		logOutput := ioutil.Discard
+		logOutput := io.Discard
 		if logFileFlag != "" {
 			f, err := os.OpenFile(logFileFlag, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 			if err != nil {