roundcube: Completely uninstall app

* remove local config and sqlite file
* add them to the backup manifest

Tests:
1. Modify the user's email address inside roundcube
2. Reinstall the app and confirm the modification was reset
3. Functional tests passed

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

plinth/modules/roundcube/__init__.py

@@ -95,6 +95,11 @@ class RoundcubeApp(app_module.App):
             privileged.set_config(local_only=True)
             self.enable()
 
+    def uninstall(self):
+        """De-configure and uninstall the app."""
+        super().uninstall()
+        privileged.uninstall()
+
     def force_upgrade(self, packages):
         """Force upgrade package to resolve conffile prompts."""
         if 'roundcube-core' not in packages:

plinth/modules/roundcube/manifest.py

@@ -10,4 +10,9 @@ clients = [{
     }]
 }]
 
-backup = {}
+backup = {
+        'data': {
+            'files': ['/etc/roundcube/freedombox-config.php',
+                      '/var/lib/dbconfig-common/sqlite3/roundcube/roundcube']
+        }
+}

plinth/modules/roundcube/privileged.py

@@ -8,6 +8,8 @@ from plinth import action_utils
 from plinth.actions import privileged
 
 _config_file = pathlib.Path('/etc/roundcube/freedombox-config.php')
+_rc_db_file = pathlib.Path('/var/lib/dbconfig-common/sqlite3/'
+                           'roundcube/roundcube')
 
 
 @privileged
@@ -68,3 +70,10 @@ $config['smtp_helo_host'] = 'localhost';
 '''
 
     _config_file.write_text(config, encoding='utf-8')
+
+
+@privileged
+def uninstall():
+    """Remove config file and database."""
+    for item in _config_file, _rc_db_file:
+        item.unlink(missing_ok=True)