Add ping stream to turbine AMQP

This change adds more data to the stream with {"type":"Ping"}
so (I believe) the existing dashboard client will discard it,
but stay alive.

Fixes gh-264

spring-cloud-netflix-turbine-amqp/src/main/java/org/springframework/cloud/netflix/turbine/amqp/TurbineAmqpConfiguration.java

@@ -21,9 +21,12 @@ import io.reactivex.netty.RxNetty;
 import io.reactivex.netty.protocol.http.server.HttpServer;
 import io.reactivex.netty.protocol.text.sse.ServerSentEvent;
 
+import java.util.Collections;
 import java.util.Map;
+import java.util.concurrent.TimeUnit;
 
 import lombok.extern.apachecommons.CommonsLog;
+
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.SmartLifecycle;
@@ -71,6 +74,11 @@ public class TurbineAmqpConfiguration implements SmartLifecycle {
 				.doOnUnsubscribe(() -> log.info("Unsubscribing aggregation."))
 				.doOnSubscribe(() -> log.info("Starting aggregation")).flatMap(o -> o)
 				.publish().refCount();
+		Observable<Map<String, Object>> ping = Observable.timer(1, 10, TimeUnit.SECONDS)
+				.map(count -> {
+					return Collections.singletonMap("type", (Object) "Ping");
+				}).publish().refCount();
+		Observable<Map<String, Object>> output = Observable.merge(publishedStreams, ping);
 
 		this.turbinePort = this.turbine.getPort();
 
@@ -83,7 +91,7 @@ public class TurbineAmqpConfiguration implements SmartLifecycle {
 				(request, response) -> {
 					log.info("SSE Request Received");
 					response.getHeaders().setHeader("Content-Type", "text/event-stream");
-					return publishedStreams.doOnUnsubscribe(
+					return output.doOnUnsubscribe(
 							() -> log.info("Unsubscribing RxNetty server connection"))
 							.flatMap(
 									data -> response.writeAndFlush(new ServerSentEvent(