test-network: disable 'no-member' warning for the Utilities class

The warning is correct, since we don't inherit the necessary
unittest.TestCase class, but that's on purpose, since the Utilities
class is not supposed to be instantiated on its own, but should
complement other classes' definitions which do inherit from the
unittest.TestCase class.

test/test-network/systemd-networkd-tests.py

@@ -586,8 +586,9 @@ def restart_networkd(sleep_sec=0, show_logs=True, remove_state_files=True):
     stop_networkd(show_logs, remove_state_files)
     start_networkd(sleep_sec)
 
-
 class Utilities():
+    # pylint: disable=no-member
+
     def check_link_exists(self, link):
         self.assertTrue(link_exists(link))