Example of how can we properly return a command's retcode

[There](https://github.com/saltstack/salt/issues/7247 "#7247") [are](https://github.com/saltstack/salt/issues/8180 "#8180") [many](https://github.com/saltstack/salt/issues/8589 "#8589") [issues](https://github.com/saltstack/salt/issues/6973 "#6973") [about](https://github.com/saltstack/salt/issues/7876 "#7876") the same thing.

I wrote an example how Salt can properly handle a command's retcode.

```
(salt_venv)user@user-salt:~/salt_venv$ salt -c ./etc/salt '*' test.ping
minion-dev:
    ----------
    comment:
        
    result:
        True
    retcode:
        1
(salt_venv)user@user-salt:~/salt_venv$ echo $?
1
```

Please review and criticize.