syncthing: Completely uninstall app

Remove config file when app is uninstalled

Tests:
1. Install app and add a share
2. Reinstall app and confirm that the share doesn't exist

The order of the functional tests should be modified
since 'test_add_remove_folder' fails

Signed-off-by: nbenedek <contact@nbenedek.me>
[sunil: Update docstrings, make uninstall fail-safe]
[sunil: Remove the entire configuration directory]
Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/modules/syncthing/__init__.py

@@ -143,3 +143,8 @@ class SyncthingApp(app_module.App):
                     sharing.remove_share(name)
                     sharing.add_share(name, share['path'], new_groups,
                                       share['is_public'])
+
+    def uninstall(self):
+        """De-configure and uninstall the app."""
+        super().uninstall()
+        privileged.uninstall()

plinth/modules/syncthing/privileged.py

@@ -3,6 +3,7 @@
 
 import grp
 import os
+import pathlib
 import pwd
 import shutil
 import subprocess
@@ -80,3 +81,9 @@ def setup_config():
 
     if conf_changed:
         action_utils.service_try_restart('syncthing@syncthing')
+
+
+@privileged
+def uninstall():
+    """Remove configuration file when app is uninstalled."""
+    shutil.rmtree(DATA_DIR + '/.config', ignore_errors=True)