use thenCompose and return future result

Signed-off-by: Gabriel Fukushima <[email protected]>

teku/src/main/java/tech/pegasys/teku/services/ServiceController.java

@@ -42,7 +42,7 @@ protected SafeFuture<?> doStop() {
     Collections.reverse(services);
     final Service storageService = services.removeFirst();
     return SafeFuture.allOf(services.stream().map(Service::stop).toArray(SafeFuture[]::new))
-        .thenRun(storageService::stop);
+        .thenCompose(__ -> SafeFuture.fromRunnable(storageService::stop));
   }
 
   @Override