Don't ever give up trying to connect to OVN DBs

It doesn't really make since to give up connectimg to the OVN DBs
since we can't do anything without them. If ovsdb-server is slow
and takes more than timeout seconds, everything reconnecting after
partial downloads and starting over is not going to make things
better.

We can change the behavior in ovsdbapp, but doing it without
making non-backportable API changes isn't easily doable.
The plan would be, after merging this back through stable, to
modify ovsdbapp to allow setting different connection and txn
timeouts and being able to disable the timeout in wait_for_change
with a value of -1. Then in the main branch of neutron we can
use that going forward.

Closes-Bug: #1926653

Change-Id: Ia9e23113fdeebf0b99085da200c3d61b71567d36
(cherry picked from commit 39ccc0d6d6)

neutron/plugins/ml2/drivers/ovn/mech_driver/ovsdb/impl_idl_ovn.py

@@ -39,6 +39,19 @@ from neutron.services.portforwarding import constants as pf_const
 LOG = log.getLogger(__name__)
 
 
+# Override wait_for_change to not use a timeout so we always try to reconnect
+def wait_for_change(idl_, timeout, seqno=None):
+    if seqno is None:
+        seqno = idl_.change_seqno
+        while idl_.change_seqno == seqno and not idl_.run():
+            poller = idlutils.poller.Poller()
+            idl_.wait(poller)
+            poller.block()
+
+
+idlutils.wait_for_change = wait_for_change
+
+
 class OvnNbTransaction(idl_trans.Transaction):
 
     def __init__(self, *args, **kwargs):

neutron/tests/functional/plugins/ml2/drivers/ovn/mech_driver/ovsdb/test_impl_idl.py

@@ -15,6 +15,7 @@
 import copy
 import uuid
 
+from ovsdbapp.backend.ovs_idl import connection
 from ovsdbapp import constants as const
 from ovsdbapp import event as ovsdb_event
 from ovsdbapp.tests.functional import base
@@ -259,3 +260,13 @@ class TestNbApi(BaseOvnIdlTest):
             lb_match = f(exp_fip_id)
             self.assertIn((lb_match['name'], lb_match['external_ids']),
                           exp_values)
+
+
+class TestIgnoreConnectionTimeout(BaseOvnIdlTest):
+    @classmethod
+    def create_connection(cls, schema):
+        idl = connection.OvsdbIdl.from_server(cls.schema_map[schema], schema)
+        return connection.Connection(idl, 0)
+
+    def test_setUp_will_fail_if_this_is_broken(self):
+        pass