Not enforcing EnableAutoConfiguration on aggregate parent

- The aggregate parent configuration now imports the required auto configuration classes such as ChannelBindingAutoConfiguration and EndpointAutoConfiguration
while `@EnableBinding` is still at the parent configuration to be able to share the binding configuration among the child applications
 - Add `ConditionalOnMissingBean` in spring cloud stream auto configuration classes so that if `EnableAutoConfiguration` is enabled at child application classes
they don't get instantiated again
 - Conditionally import EmbeddedServlet auto-configuration when web environment is enabled for parent
 - Add test

Resolves #737

spring-cloud-stream-test-support/src/test/java/org/springframework/cloud/stream/test/aggregate/AggregateTestWithMain.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 the original author or authors.
+ * Copyright 2016-2017 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.
@@ -25,6 +25,7 @@ import org.springframework.cloud.stream.aggregate.AggregateApplicationBuilder;
 import org.springframework.cloud.stream.annotation.EnableBinding;
 import org.springframework.cloud.stream.messaging.Processor;
 import org.springframework.cloud.stream.test.binder.MessageCollector;
+import org.springframework.cloud.stream.test.binder.TestSupportBinderAutoConfiguration;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.integration.annotation.Transformer;
@@ -41,7 +42,7 @@ public class AggregateTestWithMain {
 	@Test
 	public void testAggregateApplication() throws InterruptedException {
 		// emulate a main method
-		ConfigurableApplicationContext context = new AggregateApplicationBuilder().from(UppercaseProcessor.class)
+		ConfigurableApplicationContext context = new AggregateApplicationBuilder(TestSupportBinderAutoConfiguration.class).from(UppercaseProcessor.class)
 				.namespace("upper").to(SuffixProcessor.class).namespace("suffix").run();
 
 		AggregateApplication aggregateAccessor = context.getBean(AggregateApplication.class);