address missing items ...

[kif]

I noticed random crashes because the web-request did not provide all information requested ...

Traceback (most recent call last):
  File "/usr/local/sbin/fbxosctrl.py", line 1371, in <module>
    rc = cli.dispatch(args)
         ^^^^^^^^^^^^^^^^^^
  File "/usr/local/sbin/fbxosctrl.py", line 1359, in dispatch
    return self._cmd_handlers.get(cmd, self._parser.print_help)()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/sbin/fbxosctrl.py", line 615, in get_system_info
    print(' - Model:     {}'.format(resp.result['model_info']['pretty_name']))
                                    ~~~~~~~~~~~^^^^^^^^^^^^^^
KeyError: 'model_info'

For this, I replaced most of the direct item access with [] with .get() which will print nothing instead of crashing.
Beside this, I also replaced some of the old-style formatting based on .format() with f-strings (not yet everywhere) and corrected the comparison to singletons like None, True & False with is instead of =.