I originally used an await in case the setting of callbacks in the registry hadn't yet finished by the time the WatchServiceTask decides to notify the monitor actor. What do you think ? :)

According to [the 2.2.1 migration guide](http://doc.akka.io/docs/akka/current/project/migration-guide-2.1.x-2.2.x.html), the migration should be `agent.await(Timeout)` to `Await.result(agent.future, Timeout)`.