Description of problem:
Adding or removing products from a sync plan is an asynchronous task, and there's no way to monitor the progress of the task. This bites the user when:

* The user adds a product to a sync plan, then attempts to add that same product to a second sync plan.
* The user adds a product to a sync plan, removes it from the sync plan, then re-adds it.
* More scenarios?

This problem is exacerbated by the fact that product addition and deletion can take tens of seconds to complete. The solution? When a product is added to or removed from a sync plan, the satellite should return a task that can be monitored.

Version-Release number of selected component (if applicable):


How reproducible:
Very frequent, but varies depending on server load.

Steps to Reproduce:
Issue an HTTP PUT request to the following URLs. Pass in an identical list of product IDs as the JSON payload to each request:

* https://${hostname}/katello/api/v2/organizations/:organization_id/sync_plans/:sync_plan_id/add_products
* https://${hostname}/katello/api/v2/organizations/:organization_id/sync_plans/:sync_plan_id/remove_products
* https://${hostname}/katello/api/v2/organizations/:organization_id/sync_plans/:sync_plan_id/add_products

Actual results:
The server responds to product addition and removal requests with a hash of data about the sync plan being worked with.

Expected results:
The server responds to product addition and removal requests with a hash of data about the task under way.

Additional info: