Allow timeouts to be configurable

add additional options to clusterMaster config for timeouts

* `stopTimeout` - Time in milliseconds to wait for worker to stop before
  forcefully killing the process during restart or resize, default 5000
  (5 seconds)
* `skepticTimeout` - Time in milliseconds to wait for worker to live
  before shutting previous worker down during restart, default 2000
  (2 seconds)