Don't set and remove immediately DEAD VLAN tag in tests

In fullstack and functional tests where OVSPortFixture is used to create
port in OVS bridge, just after port was created by ovs interface driver,
DEAD_VLAN tag was removed from the port as it's not needed in tests.
But this could cause race condition and instead of removing DEAD_VLAN
tag, actually correct tag configured by e.g. neutron_openvswitch_agent
was removed and traffic to such port wasn't working at all.

To avoid that race, now method which adds setting DEAD_VLAN tag to the
port_replace transaction is now mocked so there will be no DEAD VLAN tag
set on such port at all.

This patch also removes unstable test decorator from the
TestDhcpAgentHA.test_multiple_agents_for_network fullstack test as it
seems for me that this was the reason why this test was failing pretty
often.

Closes-Bug: #2000150
Change-Id: I3938c94bbd531fac461e80e791c128821a4f837f

neutron/tests/common/net_helpers.py

@@ -24,6 +24,7 @@ import shlex
 import signal
 import subprocess
 import time
+from unittest import mock
 
 import fixtures
 import netaddr
@@ -880,20 +881,19 @@ class OVSPortFixture(PortFixture):
         interface_config = cfg.ConfigOpts()
         config.register_interface_opts(interface_config)
         ovs_interface = interface.OVSInterfaceDriver(interface_config)
-        ovs_interface.plug_new(
-            None,
-            self.port_id,
-            port_name,
-            self.mac,
-            bridge=self.bridge.br_name,
-            namespace=self.namespace)
-        # NOTE(mangelajo): for OVS implementations remove the DEAD VLAN tag
-        # on ports that we intend to use as fake vm interfaces, they
-        # need to be flat. This is related to lp#1767422
-        self.bridge.clear_db_attribute("Port", port_name, "tag")
-        # Clear vlan_mode that is added for each new port. lp#1930414
-        self.bridge.clear_db_attribute("Port", port_name, "vlan_mode")
-        self.bridge.clear_db_attribute("Port", port_name, "trunks")
+        # NOTE(slaweq): for OVS implementation normally there would be DEAD
+        # VLAN tag set for port and we would need to remove it here as it is
+        # needed during the tests. But to avoid setting and removing tag, we
+        # can simply mock _set_port_dead method so port will not be tagged with
+        # DEAD_VLAN tag initially
+        with mock.patch.object(ovs_lib.OVSBridge, '_set_port_dead'):
+            ovs_interface.plug_new(
+                None,
+                self.port_id,
+                port_name,
+                self.mac,
+                bridge=self.bridge.br_name,
+                namespace=self.namespace)
         self.addCleanup(self.bridge.delete_port, port_name)
         self.port = ip_lib.IPDevice(port_name, self.namespace)
 

neutron/tests/fullstack/test_dhcp_agent.py

@@ -19,7 +19,6 @@ from oslo_utils import uuidutils
 
 from neutron.agent.linux import ip_lib
 from neutron.common import utils as common_utils
-from neutron.tests import base as test_base
 from neutron.tests.fullstack.agents import dhcp_agent
 from neutron.tests.fullstack import base
 from neutron.tests.fullstack.resources import environment
@@ -185,7 +184,6 @@ class TestDhcpAgentHA(BaseDhcpAgentTest):
         # check if new vm will get IP from new DHCP agent
         self._spawn_vm()
 
-    @test_base.unstable_test('bug 2000150')
     def test_multiple_agents_for_network(self):
         network_dhcp_agents = self.client.list_dhcp_agent_hosting_networks(
             self.network['id'])['agents']