Modify dealmaking code to use sp preference

[jcace]

API Node - Dealmaking code in the content manager should first determine the closest SPs to the content's location and use that list when deciding where to make the deal.

Request the shuttle for list of shuttle preference (filtered to top 20? - configurable amount), choose one randomly from there. Look at caching the list on the API node side for a given amount of time to minimize requests to the shuttle.

[Sottomayor18]

@jcace should this be assigned to you?