fatbuildrctl crash when preferences file not present

[rezib]

When user preferences file is not present, fatbuildrctl crashes due to undefined UserPreferences.tokens_dir attribute. For example:

$ fatbuildrctl images create
Traceback (most recent call last):
  File "/usr/bin/fatbuildrctl", line 33, in <module>
    sys.exit(load_entry_point('Fatbuildr==2.0.0', 'console_scripts', 'fatbuildrctl')())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/fatbuildr/cli/__init__.py", line 34, in run
    cls()
  File "/usr/lib/python3/dist-packages/fatbuildr/cli/fatbuildrctl.py", line 437, in __init__
    args.func(args)
  File "/usr/lib/python3/dist-packages/fatbuildr/cli/fatbuildrctl.py", line 503, in _run_images
    selected_formats = self.connection.pipelines_formats()
                       ^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/fatbuildr/cli/fatbuildrctl.py", line 458, in connection
    self.uri, ClientTokensManager(self.prefs.tokens_dir).load(self.uri)
                                  ^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'UserPreferences' object has no attribute 'tokens_dir'