Reproduce bug 1917645

The [oslo_messaging_notification]retry parameter is not applied during
connecting to the message bus. But the documentation implies it should[1][2].
The two possible drivers, rabbit and kafka, behaves differently.

1) The rabbit driver will retry the connection forever, blocking the caller
   process.

2) The kafka driver also ignores the retry configuration but the
   notifier call returns immediately even if the notification is not
   (cannot) be delivered.

This patch adds test cases to show the wrong behavior.

[1] https://docs.openstack.org/oslo.messaging/latest/configuration/opts.html#oslo_messaging_notifications.retry
[2] https://github.com/openstack/oslo.messaging/blob/feb72de7b81e3919dedc697f9fb5484a92f85ad8/oslo_messaging/notify/messaging.py#L31-L36

Related-Bug: #1917645

Change-Id: Id8557050157aecd3abd75c9114d3fcaecdfc5dc9