discard umount error if directory is not mounted

if the directory is not mounted return nil
during umount of mountPoint

Discard error if error is os.IsNotExist

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>
(cherry picked from commit dcafdb519e)

pkg/util/nodecache.go

@@ -155,7 +155,7 @@ func (nc *NodeCache) Delete(identifier string) error {
 	file := path.Join(nc.BasePath, nc.CacheDir, identifier+".json")
 	err := os.Remove(file)
 	if err != nil {
-		if err == os.ErrNotExist {
+		if os.IsNotExist(err) {
 			klog.V(4).Infof("node-cache: cannot delete missing metadata storage file %s, assuming it's already deleted", file)
 			return nil
 		}