Only ensure admin state on ports that exist

The linux bridge agent was calling ensure_port_admin state
unconditionally on ports in treat_devices_added_or_updated.
This would cause it to throw an error on interfaces that
didn't exist so it would restart the entire processing loop.

If another port was being updated in the same loop before this
one, that port would experience a port status life-cycle of
DOWN->BUILD->ACTIVE->BUILD->ACTIVE
                   ^ <--- Exception in unrelated port causes cycle
                          to start over again.

This causes the bug below because the first active transition will
cause Nova to boot the VM. At this point tempest tests expect the
ports that belong to the VM to be in the ACTIVE state so it filters
Neutron port list calls with "status=ACTIVE". Therefore tempest would
not get any ports back and assume there was some kind of error with
the port and bail.

This patch just makes sure the admin state call is skipped if the port
doesn't exist and it includes a basic unit test to prevent a regression.

Closes-Bug: #1523638
Change-Id: I5330c6111cbb20bf45aec9ade7e30d34e8dd16ca

neutron/plugins/ml2/drivers/linuxbridge/agent/linuxbridge_neutron_agent.py

@@ -1061,9 +1061,10 @@ class CommonAgentLoop(service.Service):
                 # 1) An existing race with libvirt caused by the behavior of
                 #    the old implementation. See Bug #1312016
                 # 2) The new code is much more readable
-                self.mgr.ensure_port_admin_state(
-                    device,
-                    device_details['admin_state_up'])
+                if interface_plugged:
+                    self.mgr.ensure_port_admin_state(
+                        device,
+                        device_details['admin_state_up'])
                 # update plugin about port status if admin_state is up
                 if device_details['admin_state_up']:
                     if interface_plugged:

neutron/tests/unit/plugins/ml2/drivers/linuxbridge/agent/test_linuxbridge_neutron_agent.py

@@ -391,6 +391,25 @@ class TestCommonAgentLoop(base.BaseTestCase):
                                                                   'tap4']))
         agent.treat_devices_removed.assert_called_with(set(['tap1']))
 
+    def test_treat_devices_added_updated_no_local_interface(self):
+        agent = self.agent
+        mock_details = {'device': 'dev123',
+                        'port_id': 'port123',
+                        'network_id': 'net123',
+                        'admin_state_up': True,
+                        'network_type': 'vlan',
+                        'segmentation_id': 100,
+                        'physical_network': 'physnet1',
+                        'device_owner': constants.DEVICE_OWNER_NETWORK_PREFIX}
+        agent.ext_manager = mock.Mock()
+        agent.plugin_rpc = mock.Mock()
+        agent.plugin_rpc.get_devices_details_list.return_value = [mock_details]
+        agent.mgr = mock.Mock()
+        agent.mgr.plug_interface.return_value = False
+        agent.mgr.ensure_port_admin_state = mock.Mock()
+        agent.treat_devices_added_updated(set(['tap1']))
+        self.assertFalse(agent.mgr.ensure_port_admin_state.called)
+
     def test_treat_devices_added_updated_admin_state_up_true(self):
         agent = self.agent
         mock_details = {'device': 'dev123',