Backup folder under FE temp_dir is not cleaned after backup job cleaned

[wangwq10]

Here are the steps to reproduce:

1. in mysql console
   admin set frontend config("max_backup_restore_job_num_per_db"="1");
2. do one backup
   BACKUP SNAPSHOT tpch_1t.snapshot_1 TO keep_on_local ON (nation2 ) PROPERTIES ("type" = "full");
3. do another backup
   BACKUP SNAPSHOT tpch_1t.snapshot_1 TO keep_on_local ON (nation2 ) PROPERTIES ("type" = "full");
4. check in temp_dir

Except the folder can be cleaned