Change lib/spot-request-poll.js:pollSpotRequests to be a class called SpotRequestPoller

[jhford]

It would be nice not to have to pass around quite so much context for this function. Let's turn this function into a class with an interface like this:

class SpotRequestPoller {
  constructor({ec2, state, regions, runaws}) { }
  
  poll()
}

This class should make sure that the polling is done in all regions and should have a single log output to summaries the actions taken in all regions, instead of being done per region