On retained republish message adapt the QoS to the one specified during subscription (fix issue #411)

broker/src/main/java/io/moquette/spi/IMessagesStore.java

@@ -31,7 +31,7 @@ public interface IMessagesStore {
     class StoredMessage implements Serializable {
 
         private static final long serialVersionUID = 1755296138639817304L;
-        final MqttQoS m_qos;
+        private MqttQoS m_qos;
         final byte[] m_payload;
         final String m_topic;
         private boolean m_retained;
@@ -44,6 +44,11 @@ public interface IMessagesStore {
             m_topic = topic;
         }
 
+
+        public void setQos(MqttQoS qos) {
+            this.m_qos = qos;
+        }
+
         public MqttQoS getQos() {
             return m_qos;
         }