INTSAMPLES-144: Barrier Sample

JIRA: https://jira.spring.io/browse/INTSAMPLES-144

INTSAMPLES-144: Use o-c-a for Release

INTSAMPLES-144: Switch to Spring Boot

INTSAMPLES-144: Polishing

* Upgrade to SI-4.2, SF-4.2, Boot-1.3
* Fix: https://jira.spring.io/browse/INTSAMPLES-145

basic/barrier/README.md

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+Barrier Sample
+==============
+
+This example demonstrates the use of a process barrier component to suspend a thread until some asynchronous operation 
+completes. It uses an **HTTP Inbound Gateway**, splits the request, sends the splits to rabbitmq and then waits for
+the publisher confirms. Finally, the results are returned to the caller.
+
+The sample is a Spring Boot application that loads 2 contexts:
+
+* Client - Sends **A,B,C** to the server
+* Server - Web application
+
+The server context has 3 integration flows:
+
+```
+http -> splitter -> amqp
+     |-> barrier
+
+amqp(Acks) -> aggregator -> barrier (release)
+
+qmqp(inbound) -> nullChannel
+```
+
+The last flow drains the messages and allows the auto-delete queue to be removed when the application is closed.
+
+## Running the sample
+
+
+    $ gradlew :barrier:run
+
+This will package the application and run it using the [Gradle Application Plugin](http://www.gradle.org/docs/current/userguide/application_plugin.html)
+
+#### Using an IDE such as SpringSource Tool Suite™ (STS)
+
+In STS (Eclipse), go to package **org.springframework.integration.samples.barrier**, right-click **Application** and select **Run as** --> **Java Application** (or Spring Boot Application).
+
+### Output
+  
+The gateway (**client**) initiates a simple request posting "A,B,C" to the **server** and the **server** responds with the results.
+You should see the following output from the server:
+   
+    ++++++++++++ Replied with: Result: A: ack=true, B: ack=true, C: ack=true ++++++++++++
+
+