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/fs-v1-rwpool_test.go

@@ -18,7 +18,6 @@
 package cmd
 
 import (
-	"os"
 	"runtime"
 	"testing"
 
@@ -48,11 +47,10 @@ func TestRWPoolLongPath(t *testing.T) {
 // Tests all RWPool methods.
 func TestRWPool(t *testing.T) {
 	// create xlStorage test setup
-	_, path, err := newXLStorageTestSetup()
+	_, path, err := newXLStorageTestSetup(t)
 	if err != nil {
 		t.Fatalf("Unable to create xlStorage test setup, %s", err)
 	}
-	defer os.RemoveAll(path)
 
 	rwPool := &fsIOPool{
 		readersMap: make(map[string]*lock.RLockedFile),