Fix network list functional test

An error in network func test broke our CI,
looks like the "is_default" should be "False"
by default for now.

Change-Id: I021eb8abd9bdf55c7c06031152c107312f104b34

openstackclient/tests/functional/network/v2/test_network.py

@@ -181,7 +181,7 @@ class NetworkTests(base.TestCase):
             cmd_output["shared"],
         )
         self.assertEqual(
-            None,
+            False,
             cmd_output["is_default"],
         )
         self.assertEqual(