[ovn]neutron agent show real heartbeat_timestamp

agent's heartbeat_timestamp returns the current time, not
conducive to agent status troubleshooting.
this patch use agent's updated_at as heartbeat_timestamp.

Closes-bug: #1977629

Change-Id: Idf522a20f9735829ee568020bfed46345a95e294
(cherry picked from commit 411ecc4)

Author: zhouhenglc

neutron/plugins/ml2/drivers/ovn/agent/neutron_agent.py

@@ -82,7 +82,7 @@ def as_dict(self):
         return {
             'binary': self.binary,
             'host': self.chassis.hostname,
-            'heartbeat_timestamp': timeutils.utcnow(),
+            'heartbeat_timestamp': self.updated_at,
             'availability_zone': ', '.join(
                 ovn_utils.get_chassis_availability_zones(self.chassis)),
             'topic': 'n/a',

neutron/tests/functional/plugins/ml2/drivers/ovn/mech_driver/test_mech_driver.py

@@ -13,8 +13,10 @@
 #    under the License.
 
 import copy
+import datetime
 import functools
 import re
+import time
 from unittest import mock
 
 import netaddr
@@ -1054,6 +1056,25 @@ def test_agent_show(self):
         for agent_id in self.agent_types.values():
             self.assertTrue(self.plugin.get_agent(self.context, agent_id))
 
+    def test_agent_show_real_heartbeat_timestamp(self):
+        agent_id = self.agent_types[ovn_const.OVN_CONTROLLER_AGENT]
+        agent = self.plugin.get_agent(self.context, agent_id)
+        heartbeat_timestamp = agent['heartbeat_timestamp']
+        if self.sb_api.is_table_present('Chassis_Private'):
+            chassis_ts = self.sb_api.db_get(
+                'Chassis_Private', self.chassis, 'nb_cfg_timestamp'
+            ).execute(check_error=True)
+            updated_at = datetime.datetime.fromtimestamp(
+                int(chassis_ts / 1000), datetime.timezone.utc)
+            # if table Chassis_Private present, agent.updated_at is
+            # Chassis_Private.nb_cfg_timestamp
+            self.assertEqual(updated_at, heartbeat_timestamp)
+        time.sleep(1)
+        # if chassis is not updated, agent's heartbeat_timestamp shouldn't
+        # be updated.
+        n_agent = self.plugin.get_agent(self.context, agent['id'])
+        self.assertEqual(heartbeat_timestamp, n_agent['heartbeat_timestamp'])
+
     def test_agent_list(self):
         agent_ids = [a['id'] for a in self.plugin.get_agents(
             self.context, filters={'host': self.host})]