Fix MQTT reconnection and add some debug logging (openhab#1254)

Signed-off-by: Jan N. Klug <jan.n.klug@rub.de>

bundles/org.openhab.core.io.transport.mqtt/src/main/java/org/eclipse/smarthome/io/transport/mqtt/MqttBrokerConnection.java

@@ -172,9 +172,10 @@ public void onDisconnected(Throwable t) {
  // If we tried to connect via start(), use the reconnect strategy to try it again
  if (connection.isConnecting) {
  connection.isConnecting = false;
- if (connection.reconnectStrategy != null) {
- connection.reconnectStrategy.lostConnection();
- }
+ }
+
+ if (connection.reconnectStrategy != null) {
+ connection.reconnectStrategy.lostConnection();
  }
  }
 
@@ -562,6 +563,7 @@ public CompletableFuture<Boolean> subscribe(String topic, MqttMessageSubscriber
  if (client.getState().isConnected()) {
  client.subscribe(topic, qos, clientCallback).whenComplete((s, t) -> {
  if (t == null) {
+ logger.trace("Subscribed {} to topic {}", subscriber, topic);
  future.complete(true);
  } else {
  future.completeExceptionally(new MqttException(t));
@@ -612,17 +614,20 @@ public CompletableFuture<Boolean> unsubscribe(String topic, MqttMessageSubscribe
  synchronized (subscribers) {
  final @Nullable List<MqttMessageSubscriber> list = subscribers.get(topic);
  if (list == null) {
+ logger.trace("Tried to unsubscribe {} from topic {}, but subscriber list is empty", subscriber, topic);
  return CompletableFuture.completedFuture(true);
  }
  list.remove(subscriber);
  if (!list.isEmpty()) {
+ logger.trace("Removed {} from topic subscribers for topic {}, but other subscribers present", subscriber, topic);
  return CompletableFuture.completedFuture(true);
  }
  // Remove from subscriber list
  subscribers.remove(topic);
  // No more subscribers to this topic. Unsubscribe topic on the broker
  MqttAsyncClientWrapper mqttClient = this.client;
  if (mqttClient != null) {
+ logger.trace("Subscriber list is empty after removing {}, unsubscribing topic {} from connection", subscriber, topic);
  return unsubscribeRaw(mqttClient, topic);
  } else {
  return CompletableFuture.completedFuture(false);