Add WaitForPortCreateEvent in BaseOVSTestCase

When a port is created, the test case will wait until the IDL event
is raised and the port is effectively created and the local DB
cache is updated.

Conflicts:
      neutron/tests/functional/agent/common/test_ovs_lib.py

Change-Id: I660baccde67a040731538276fc6dff05a10efb68
Related-Bug: #1910717
(cherry picked from commit e0f15c5982)

neutron/tests/functional/agent/common/test_ovs_lib.py

@@ -18,6 +18,7 @@ import functools
 import mock
 from neutron_lib.services.qos import constants as qos_constants
 from oslo_utils import uuidutils
+from ovsdbapp.backend.ovs_idl import event
 import six
 
 from neutron.agent.common import ovs_lib
@@ -37,6 +38,17 @@ OTHER_CONFIG_DEFAULT = {six.u('max-rate'): six.u(str(MAX_RATE_DEFAULT)),
                         six.u('min-rate'): six.u(str(MIN_RATE_DEFAULT))}
 
 
+class WaitForPortCreateEvent(event.WaitEvent):
+    event_name = 'WaitForPortCreateEvent'
+
+    def __init__(self, port_name):
+        table = 'Port'
+        events = (self.ROW_CREATE,)
+        conditions = (('name', '=', port_name),)
+        super(WaitForPortCreateEvent, self).__init__(
+            events, table, conditions, timeout=5)
+
+
 class BaseOVSTestCase(base.BaseSudoTestCase):
 
     def setUp(self):
@@ -111,8 +123,11 @@ class BaseOVSTestCase(base.BaseSudoTestCase):
         self.elements_to_clean['bridges'].append(self.br_name)
 
     def _create_port(self, port_name):
+        row_event = WaitForPortCreateEvent(port_name)
+        self.ovs.ovsdb.idl.notify_handler.watch_event(row_event)
         self.ovs.ovsdb.add_port(self.br_name, port_name).execute(
             check_error=True)
+        self.assertTrue(row_event.wait())
 
     def _find_port_uuid(self, port_name):
         return self.ovs.ovsdb.db_get('Port', port_name, '_uuid').execute()