[ccplugin] celery-monitor: retry failed items
When multiple instance of celery-monitor are running, we could have an integrity errors raised if two instance are working on the same task_id or temporary (network, host) failures. In this case we want to retry handling the task_id later. Put pending processed task_id in a "pending queue" and each minutes and if the monitor queue is empty, requeue pending items. This change require to handle the "timeout" parameter of loop (only used in tests) in a different way to ensure not blocking forever in redis "brpoplpush".