test: use T.TempDir to create temporary test directory (#15400)

This commit replaces `ioutil.TempDir` with `t.TempDir` in tests. The
directory created by `t.TempDir` is automatically removed when the test
and all its subtests complete.

Prior to this commit, temporary directory created using `ioutil.TempDir`
needs to be removed manually by calling `os.RemoveAll`, which is omitted
in some tests. The error handling boilerplate e.g.
	defer func() {
		if err := os.RemoveAll(dir); err != nil {
			t.Fatal(err)
		}
	}
is also tedious, but `t.TempDir` handles this for us nicely.

Reference: https://pkg.go.dev/testing#T.TempDir

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

cmd/object-api-listobjects_test.go

@@ -23,8 +23,6 @@ import (
 	"crypto/md5"
 	"encoding/hex"
 	"fmt"
-	"io/ioutil"
-	"os"
 	"strconv"
 	"strings"
 	"testing"
@@ -1886,18 +1884,14 @@ func initFSObjectsB(disk string, t *testing.B) (obj ObjectLayer) {
 // BenchmarkListObjects - Run ListObject Repeatedly and benchmark.
 func BenchmarkListObjects(b *testing.B) {
 	// Make a temporary directory to use as the obj.
-	directory, err := ioutil.TempDir(globalTestTmpDir, "minio-list-benchmark")
-	if err != nil {
-		b.Fatal(err)
-	}
-	defer os.RemoveAll(directory)
+	directory := b.TempDir()
 
 	// Create the obj.
 	obj := initFSObjectsB(directory, b)
 
 	bucket := "ls-benchmark-bucket"
 	// Create a bucket.
-	err = obj.MakeBucketWithLocation(context.Background(), bucket, BucketOptions{})
+	err := obj.MakeBucketWithLocation(context.Background(), bucket, BucketOptions{})
 	if err != nil {
 		b.Fatal(err)
 	}