chore: fix python lint warnings (#14638)

* chore: fix lint warnings

* chore: another try at python import errors

Looks like the problem is that dbus_mock.py is running as
a script but living in the `lib/` directory where it's part of a
module. Moving it up into the `script/` directory seems to
solve the issue.

script/dbus_mock.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python
+
+import atexit
+import os
+import subprocess
+import sys
+
+from dbusmock import DBusTestCase
+
+from lib.config import is_verbose_mode
+
+def stop():
+    DBusTestCase.stop_dbus(DBusTestCase.system_bus_pid)
+    DBusTestCase.stop_dbus(DBusTestCase.session_bus_pid)
+
+def start():
+    log = sys.stdout if is_verbose_mode() else open(os.devnull, 'w')
+
+    DBusTestCase.start_system_bus()
+    DBusTestCase.spawn_server_template('logind', None, log)
+
+    DBusTestCase.start_session_bus()
+    DBusTestCase.spawn_server_template('notification_daemon', None, log)
+
+if __name__ == '__main__':
+    start()
+    try:
+        print(sys.argv)
+        subprocess.check_call(sys.argv[1:])
+    finally:
+        stop()