GH-85: Add SqsMDChannelAdapter.getQueue()

Fixes spring-projects/spring-integration-aws#85

* For better component management add
`SqsMessageDrivenChannelAdapter.getQueue()` to return what queues this
channel adapter is subscribed
* Upgrade to Gradle 4.6 and Checkstyle 8.8

src/test/java/org/springframework/integration/aws/inbound/SqsMessageDrivenChannelAdapterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2017 the original author or authors.
+ * Copyright 2015-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -108,6 +108,8 @@ public class SqsMessageDrivenChannelAdapterTests {
 				this.controlBusInput.send(new GenericMessage<>("@sqsMessageDrivenChannelAdapter.start('foo')")))
 				.hasCauseExactlyInstanceOf(IllegalArgumentException.class)
 				.hasMessageContaining("Queue with name 'foo' does not exist");
+
+		assertThat(this.sqsMessageDrivenChannelAdapter.getQueues()).isEqualTo(new String[] { "testQueue" });
 	}
 
 	@Configuration