remove context_manager from neutron

The context_manager is already in neutron-lib and being used by our
active consumers either directly or via the current shim we have
in neutron.db.api.context_manager that just references that in lib.
This patch removes the context_manager from neutron and updates the UTs
that mock it.

NeutronLibImpact

Change-Id: Ia5191a71b377e2862592a09da8dc3a5d415de9aa

neutron/db/api.py

@@ -15,16 +15,12 @@
 
 import weakref
 
-from neutron_lib.db import api
 from neutron_lib.db import model_base
 import sqlalchemy
 from sqlalchemy import event  # noqa
 from sqlalchemy import orm
 
 
-context_manager = api.get_context_manager()
-
-
 # Expire relationships when foreign key changes.
 #
 # NOTE(ihrachys) Arguably, it's a sqlalchemy anti-pattern to access child

neutron/service.py

@@ -21,6 +21,7 @@ from neutron_lib.callbacks import events
 from neutron_lib.callbacks import registry
 from neutron_lib.callbacks import resources
 from neutron_lib import context
+from neutron_lib.db import api as session
 from neutron_lib.plugins import directory
 from neutron_lib import worker as neutron_worker
 from oslo_concurrency import processutils
@@ -36,7 +37,6 @@ from neutron.common import config
 from neutron.common import profiler
 from neutron.common import rpc as n_rpc
 from neutron.conf import service
-from neutron.db import api as session
 from neutron import wsgi
 
 
@@ -244,7 +244,7 @@ def _start_workers(workers):
             # dispose the whole pool before os.fork, otherwise there will
             # be shared DB connections in child processes which may cause
             # DB errors.
-            session.context_manager.dispose_pool()
+            session.get_context_manager().dispose_pool()
 
             for worker in process_workers:
                 worker_launcher.launch_service(worker,

neutron/tests/unit/test_wsgi.py

@@ -18,6 +18,7 @@ import socket
 import ssl
 
 import mock
+from neutron_lib.db import api as db_api
 from neutron_lib import exceptions as exception
 from oslo_config import cfg
 from six.moves import urllib
@@ -68,7 +69,7 @@ class TestServiceBase(base.BaseTestCase):
 class TestWorkerService(TestServiceBase):
     """WorkerService tests."""
 
-    @mock.patch('neutron.db.api.context_manager.get_legacy_facade')
+    @mock.patch.object(db_api, 'get_context_manager')
     def test_start_withoutdb_call(self, apimock):
         _service = mock.Mock()
         _service.pool.spawn.return_value = None