Messages get ack'd when there is a failure and not requeued

[Luis Pigueiras]

The `ack_on_event_error` is not working for me, it doesn't requeue the messages, it ack'd then. So everytime there is a failure in the backend, I will lose messages as they get consumed anyway.

My configuration file is:

```
[DEFAULT]
http_timeout=600
log_dir=/var/log/ceilometer
rpc_backend=rabbit
transport_url=rabbit://xxx@yyy:5672/
debug=true
verbose=true

[notification]
ack_on_event_error=False <-- This option
store_events=False

[oslo_messaging_notifications]
topics=notifications
```

I propesed a patch in: https://review.openstack.org/#/c/508454/. The reason why I think that's the problem is because in this line: https://github.com/openstack/ceilometer/blob/ad933a0b63c4965db3ecf504c4f2ea1b49950d22/ceilometer/event/endpoint.py#L56, it is expected a `REQUEUE` when there is a failure if the `ack_on_event_error` is false, but this doesn't happen if the `allow_requeue` option is set to false because of: https://github.com/openstack/oslo.messaging/blob/a07d852b237d229a0f4dd55fd83379c0581e44e9/oslo_messaging/notify/listener.py#L199

[Luis Pigueiras (lpigueiras)]

Not sure if #1486660 is realated to this though

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/508454
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=35d501c4d85734a4e5741cc79cae51578e5ea379
Submitter: Zuul
Branch: master

commit 35d501c4d85734a4e5741cc79cae51578e5ea379
Author: Luis Pigueiras <email address hidden>
Date: Fri Sep 29 11:04:53 2017 +0200

    Allow requeues in when there is a failure in EventsNotificationEndpoint

    When `ack_on_event_error` is set to False, it ack's the notification
    anyway. The reason behind this is the configuration of the batch
    notification listener which doesn't allow requeues

    Change-Id: I5511272c4dc2d5759cab8b9e695bbd9ed6a1bf6a
    Closes-Bug: #1720329

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/ceilometer 11.0.0 release.