Load FIP information during initialize not init

DvrLocalRouter._load_used_fip_information() is called during the class
init however in some cases it tries to access a network namespace which
hasn't yet been created. This results in NetworkNamespaceNotFound.

This change ensures that we instead create any FIP priority rules after
the network namespace has been created by calling
_load_used_fip_information() from the initialize function rather than
in the class instantiation.

Closes-Bug: #2025129
Change-Id: I41ffffeca433faab2244ff3d1876ca078ce5ebfb
(cherry picked from commit c8c74f1)

Author: adamoswick

neutron/agent/l3/dvr_local_router.py

@@ -47,6 +47,9 @@ def __init__(self, host, *args, **kwargs):
         self.rtr_fip_connect = False
         self.fip_ns = None
         self._pending_arp_set = set()
+
+    def initialize(self, process_monitor):
+        super().initialize(process_monitor)
         self._load_used_fip_information()
 
     def _load_used_fip_information(self):

neutron/tests/unit/agent/l3/test_dvr_local_router.py

@@ -287,6 +287,15 @@ def test__load_used_fip_information(self, mock_add_ip_rule):
         self.assertEqual(sorted(ret, key=lambda ret: ret[0]),
                          fip_rule_prio_list)
 
+    @mock.patch.object(router_info.RouterInfo, 'initialize')
+    def test_initialize_dvr_local_router(self, super_initialize):
+        ri = self._create_router()
+        self.mock_load_fip.assert_not_called()
+
+        ri.initialize(self.process_monitor)
+        super_initialize.assert_called_once_with(self.process_monitor)
+        self.mock_load_fip.assert_called_once()
+
     def test_get_floating_ips_dvr(self):
         router = mock.MagicMock()
         router.get.return_value = [{'host': HOSTNAME},