Convert the block propagation and service discovery requests into CompletableFuture

[fernandohackbart]

• Java 8 CompletableFuture
  https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/package-summary.html
  http://www.deadcoderising.com/java8-writing-asynchronous-code-with-completablefuture/
  http://www.nurkiewicz.com/2013/05/java-8-definitive-guide-to.html
  https://docs.oracle.com/javase/8/docs/technotes/guides/concurrency/
  http://www.baeldung.com/java-completablefuture