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>

mount/fmountat_linux_test.go

@@ -17,7 +17,6 @@
 package mount
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"syscall"
@@ -46,7 +45,7 @@ func makeTestForFMountat(fn fMountatCaseFunc) func(t *testing.T) {
 	return func(t *testing.T) {
 		t.Parallel()
 
-		suiteDir, err := ioutil.TempDir("", "fmountat-test-")
+		suiteDir, err := os.MkdirTemp("", "fmountat-test-")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -94,7 +93,7 @@ func testFMountatNormal(t *testing.T, root string) {
 	defer umount(t, fsdir)
 
 	// check hi file
-	content, err := ioutil.ReadFile(filepath.Join(fsdir, "hi"))
+	content, err := os.ReadFile(filepath.Join(fsdir, "hi"))
 	if err != nil {
 		t.Fatalf("failed to read file: %+v", err)
 	}