Refetch local configuration on nxdrive_home change

Problem

Content of $HOME/.nuxeo-drive/config.ini (1):

[DEFAULT]
env = oauth
[oauth]
nxdrive_home = /users/tiger-222/desktop/alternate-home

Content of /users/tiger-222/desktop/alternate-home/config.ini (2):

[DEFAULT]
env = features

[features]
feature_synchronization = True

When Drive starts, it will check the (1) config file and see that another nxdrive_home folder should be used. The change is applied directly.

Then the user will be surprised because the synchronization will not be enabled. One will try to re-enable the feature and restart Drive. Same results.

Analysis

When saving features states, save_config() will use the path returned by get_config_path() and it is Options.nxdrive_home / "config.ini". So the config file is written to (2), and this is the exected behavior.

Fix

When nxdrive_home is changed, we should also fecth the eventual config.ini from the new folder to update options.

To prevent circular issues (when the new config file also set nxdrive_home, which would be crazy though) we will only fetch config file when nxdrive_home changes 1 time.