Exception on quiting

```
Traceback (most recent call last):
  File "net_diag/network_diag.py", line 442, in <module>
  File "net_diag/network_diag.py", line 437, in run
  File "net_diag/network_diag.py", line 399, in run
  File "net_diag/network_diag.py", line 422, in exit
NameError: name 'exit' is not defined
[PYI-3848:ERROR] Failed to execute script 'network_diag' due to unhandled exception!
```