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/io_util.go

@@ -38,7 +38,7 @@ func NewIOHandler() IoUtil {
 }
 
 func (handler *osIOHandler) ReadFile(filename string) ([]byte, error) {
-	return ioutil.ReadFile(filename)
+	return os.ReadFile(filename)
 }
 func (handler *osIOHandler) ReadDir(dirname string) ([]os.FileInfo, error) {
 	return ioutil.ReadDir(dirname)