Minor shell cleanups

Remove some duplication, and determine the script name from $0 instead of hardcoding it.
This command is failed, because `$ARC_DIR` is not exists.
Please add `-p`

example 

```bash
$  export ARC_DIR=arc_dir

$ mkdir $ARC_DIR/{plugins,jobs,users}
mkdir: arc_dir: No such file or directory
mkdir: arc_dir: No such file or directory
mkdir: arc_dir: No such file or directory

$ mkdir -p $ARC_DIR/{plugins,jobs,users}

$ ls -l
total 0
drwxr-xr-x  5 sueyoshi_go  staff  170 10 31 09:55 arc_dir

$ ls -l arc_dir/
total 0
drwxr-xr-x  2 sueyoshi_go  staff  68 10 31 09:55 jobs
drwxr-xr-x  2 sueyoshi_go  staff  68 10 31 09:55 plugins
drwxr-xr-x  2 sueyoshi_go  staff  68 10 31 09:55 users
```