Gardening: Simplify Node.addService

Use Mono.fromRunnable() instead of Mono.defer()

Change-Id: Ia6775c5004371c4f6b7226e283105e7334a89228
Reviewed-on: https://review.couchbase.org/c/couchbase-jvm-clients/+/208837
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Michael Reiche <michael.reiche@couchbase.com>

core-io/src/main/java/com/couchbase/client/core/node/Node.java

@@ -222,14 +222,14 @@ public synchronized Mono<Void> disconnect() {
    */
   public synchronized Mono<Void> addService(final ServiceType type, final int port,
                                             final Optional<String> bucket) {
-    return Mono.defer(() -> {
+    return Mono.fromRunnable(() -> {
       if (disconnect.get()) {
         ctx.environment().eventBus().publish(new ServiceAddIgnoredEvent(
           Event.Severity.DEBUG,
           ServiceAddIgnoredEvent.Reason.DISCONNECTED,
           ctx
         ));
-        return Mono.empty();
+        return;
       }
 
       String name = type.scope() == ServiceScope.CLUSTER ? GLOBAL_SCOPE : bucket.orElse(BUCKET_GLOBAL_SCOPE);
@@ -250,15 +250,14 @@ public synchronized Mono<Void> addService(final ServiceType type, final int port
         ctx.environment().eventBus().publish(
           new ServiceAddedEvent(Duration.ofNanos(end - start), service.context())
         );
-        return Mono.empty();
-      } else {
-        ctx.environment().eventBus().publish(new ServiceAddIgnoredEvent(
-          Event.Severity.VERBOSE,
-          ServiceAddIgnoredEvent.Reason.ALREADY_ADDED,
-          ctx
-        ));
-        return Mono.empty();
+        return;
       }
+
+      ctx.environment().eventBus().publish(new ServiceAddIgnoredEvent(
+        Event.Severity.VERBOSE,
+        ServiceAddIgnoredEvent.Reason.ALREADY_ADDED,
+        ctx
+      ));
     });
   }