INT-3437 MQTT - Support Cluster Connection

JIRA: https://jira.spring.io/browse/INT-3437

Note: Tests are still ignored due to hung connection
on close problem.

INT-3437 Polishing - PR Comments

src/reference/docbook/mqtt.xml

@@ -55,7 +55,15 @@
 				The client id.
 			</callout>
 			<callout arearefs="mqtt-i-02">
-				The broker URL.
+				<para>
+					The broker URL.
+				</para>
+				<note>
+					Starting with <emphasis>version 4.1</emphasis> the url can be omitted and, instead,
+					the server URIs can be provided in the <code>serverURIs</code> property of the
+					<classname>DefaultMqttPahoClientFactory</classname>. This enables, for example,
+					connection to a highly available (HA) cluster.
+				</note>
 			</callout>
 			<callout arearefs="mqtt-i-03">
 				A comma delimited list of topics from which this adapter will receive messages.
@@ -112,7 +120,15 @@
 				The client id.
 			</callout>
 			<callout arearefs="mqtt-o-02">
-				The broker URL.
+				<para>
+					The broker URL.
+				</para>
+				<note>
+					Starting with <emphasis>version 4.1</emphasis> the url can be omitted and, instead,
+					the server URIs can be provided in the <code>serverURIs</code> property of the
+					<classname>DefaultMqttPahoClientFactory</classname>. This enables, for example,
+					connection to a highly available (HA) cluster.
+				</note>
 			</callout>
 			<callout arearefs="mqtt-o-03">
 				An <interfacename>MqttMessageConverter</interfacename> (optional). The default

src/reference/docbook/whats-new.xml

@@ -54,5 +54,13 @@
 				See <xref linkend="http-namespace"/> for more information.
 			</para>
 		</section>
+		<section id="4.1-mqtt-cluster">
+			<title>MQTT Adapter Changes</title>
+			<para>
+				The MQTT channel adapters can now be configured to connect to multiple servers,
+				for example, to support High Availability (HA).
+				See <xref linkend="mqtt"/> for more information.
+			</para>
+		</section>
 	</section>
 </chapter>