Fix memory leak in the haproxy provider driver

The haproxy provider driver uses a dict for caching load balancer
resources (including children resources). That alone already increases
memory consumption. A neutron-server restart solves this.

But the real issue is that the driver leaves some data behind when a LB
is deleted without freeing it up (unless neutron-server is restart)
hence the memory leak.

Story: 2003802
Task: 26534

Change-Id: I7c79271998d839c6afbeb6d92f888f6acd67704e
(cherry picked from commit 111d0b2852)

neutron_lbaas/drivers/haproxy/namespace_driver.py

@@ -178,6 +178,9 @@ class HaproxyNSDriver(agent_device_driver.AgentDeviceDriver):
             ns = ip_lib.IPWrapper(namespace=namespace)
             ns.garbage_collect_namespace()
 
+        if loadbalancer_id in self.deployed_loadbalancers:
+            del self.deployed_loadbalancers[loadbalancer_id]
+
     def remove_orphans(self, known_loadbalancer_ids):
         if not os.path.exists(self.state_path):
             return

neutron_lbaas/tests/unit/drivers/haproxy/test_namespace_driver.py

@@ -108,6 +108,7 @@ class TestHaproxyNSDriver(base.BaseTestCase):
                                                        namespace=ns)
         mock_shutil.assert_called_once_with('/path/' + self.lb.id)
         mock_ns.garbage_collect_namespace.assert_called_once_with()
+        self.assertDictEqual(self.driver.deployed_loadbalancers, {})
 
     @mock.patch('os.makedirs')
     @mock.patch('os.path.dirname')