storage: stop using deprecated io/ioutil

This replaces deprecated ioutil variables and functions as follows:

* ioutil.ReadDir -> os.ReadDir
* ioutil.ReadFile -> os.ReadFile
* ioutil.TempDir -> os.MkdirTemp
* ioutil.TempFile -> os.CreateTemp
* ioutil.WriteFile -> os.WriteFile

The ReadDir conversion involves an API change, the replacement
function returns a slice of fs.DirEntry instead of fs.FileInfo.
Where appropriate, the surrounding code has been adjusted; mostly,
that means using DirEntry.Type() instead of FileInfo.Mode().
Applying this change to the IoUtil interface would mean changing its
API, so this is left for later.

Signed-off-by: Stephen Kitt <skitt@redhat.com>

pkg/volume/util/nested_volumes_test.go

@@ -17,7 +17,6 @@ limitations under the License.
 package util
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -202,7 +201,7 @@ func TestGetNestedMountpoints(t *testing.T) {
 		},
 	}
 	for _, test := range tc {
-		dir, err := ioutil.TempDir("", "TestMakeNestedMountpoints.")
+		dir, err := os.MkdirTemp("", "TestMakeNestedMountpoints.")
 		if err != nil {
 			t.Errorf("Unexpected error trying to create temp directory: %v", err)
 			return