Number of Workers in CeleryExecutor #44

num_workers is not honored by the CeleryExecutor.

There are numerous technical issues preventing this mechanism from working in the celery case.

Two potential workarounds include:

• Wrapping a task in a chain to make it count as multiple tasks. This will effectively decrease the concurrency rate with respect to a specific task.
• Create multiple routes/keys/queues and run multiple celery worker parents, one for each queue. This has an increased overhead as more worker parents are added.