Fix the Backend class for ovsbapp index changes

The Backend class in ovsdbapp was modified when adding index
support. Different projects wanted different scopes for their
ovsdb_connections, and this was moved to a property in ovsdbapp.
For now, we can just set ovsdb_connection = None on the backend
class to get the behavior we desire.

Also mocks out autocreate_indicies for a unit test.

Change-Id: I7741a441a55e67354bc0887e5db2f8137073b5b4

ovn_octavia_provider/ovsdb/impl_idl_ovn.py

@@ -50,6 +50,7 @@ class OvnNbTransaction(idl_trans.Transaction):
 # and therefor allows networking-ovn to manage connection scope on its own
 class Backend(ovs_idl.Backend):
     lookup_table = {}
+    ovsdb_connection = None
 
     def __init__(self, connection):
         self.ovsdb_connection = connection

ovn_octavia_provider/tests/unit/ovsdb/test_impl_idl_ovn.py

@@ -17,6 +17,7 @@ from unittest import mock
 
 from neutron.tests import base
 from ovs.db import idl as ovs_idl
+from ovsdbapp.backend import ovs_idl as real_ovs_idl
 from ovsdbapp.backend.ovs_idl import idlutils
 
 from ovn_octavia_provider.ovsdb import impl_idl_ovn
@@ -47,6 +48,8 @@ class TestOvnNbIdlForLb(base.BaseTestCase):
         self.idl._get_ovsdb_helper('foo')
         self.mock_gsh.assert_called_once_with('foo', 'OVN_Northbound')
 
+    @mock.patch.object(real_ovs_idl.Backend, 'autocreate_indices', mock.Mock(),
+                       create=True)
     def test_start(self):
         with mock.patch('ovsdbapp.backend.ovs_idl.connection.Connection',
                         side_effect=lambda x, timeout: mock.Mock()):