Put monitors dictionary back in MetadataDriverBase class

When the common Metadata Driver was created in [0], the
monitors dictionary was dropped accidentally. This causes
tracebacks in the fullstack L3-HA tests when
after_router_updated() is called. Put it back along with
its related tests.

[0] https://review.opendev.org/c/openstack/neutron/+/894399

Closes-bug: #2065145
Change-Id: I137ed7cec9e0eafdb3a351e5a414f5a0c16f33e5

neutron/agent/metadata/driver_base.py

@@ -159,6 +159,8 @@ class HaproxyConfiguratorBase(object):
 
 
 class MetadataDriverBase(object, metaclass=abc.ABCMeta):
+    monitors = {}
+
     @staticmethod
     @abc.abstractmethod
     def haproxy_configurator():
@@ -253,6 +255,8 @@ class MetadataDriverBase(object, metaclass=abc.ABCMeta):
             return
         monitor.register(uuid, METADATA_SERVICE_NAME, pm)
 
+        cls.monitors[uuid] = pm
+
     @classmethod
     def destroy_monitored_metadata_proxy(cls, monitor, uuid, conf, ns_name):
         monitor.unregister(uuid, METADATA_SERVICE_NAME)
@@ -272,6 +276,8 @@ class MetadataDriverBase(object, metaclass=abc.ABCMeta):
         configurator = cls.haproxy_configurator()
         configurator.cleanup_config_file(uuid, cfg.CONF.state_path)
 
+        cls.monitors.pop(uuid, None)
+
     @classmethod
     def _get_metadata_proxy_process_manager(cls, router_id, conf, ns_name=None,
                                             callback=None):

neutron/tests/unit/agent/metadata/test_driver.py

@@ -312,6 +312,7 @@ class TestMetadataDriverProcess(base.BaseTestCase):
                 network_id=network_id)
         error_log.assert_called_once()
         process_monitor.register.assert_not_called()
+        self.assertNotIn(network_id, metadata_driver.MetadataDriver.monitors)
 
     def test_create_config_file_wrong_user(self):
         with mock.patch('pwd.getpwnam', side_effect=KeyError):

neutron/tests/unit/agent/ovn/metadata/test_driver.py

@@ -197,6 +197,7 @@ class TestMetadataDriverProcess(base.BaseTestCase):
 
         error_log.assert_called_once()
         process_monitor.register.assert_not_called()
+        self.assertNotIn(network_id, metadata_driver.MetadataDriver.monitors)
 
     def test_create_config_file_wrong_user(self):
         with mock.patch('pwd.getpwnam', side_effect=KeyError):