code: public CompletesEventually completesFor(final Address address, final Completes<?> clientCompletes) {
      return completesProviderKeeper.findDefault().provideCompletesFor(address, clientCompletes);
    }
docs: Answers a {@code CompletesEventually} instance identified by {@code address} that backs the {@code clientCompletes}.
  This manages the {@code Completes} using the {@code CompletesEventually} plugin {@code Actor} pool.
  @param address the {@code Address} of the CompletesEventually actor to reuse
  @param clientCompletes the {@code CompletesEventually} allocated for eventual completion of {@code clientCompletes}
  @return CompletesEventually