Align expectations of various JMX configurations

They all want to create an MBeanServer and when that happens
user sees no MBeans, or sometimes just one set (Spring Core,
Spring Integration or Spring Boot). To harmonise them we
create a @Bean of type MBeanServer and link to it in the
other autoconfigs

Fixes gh-1046

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -1688,6 +1688,17 @@ infrastructure to receive messages asynchronously. Spring AMQP provides a simila
 feature set for the ``Advanced Message Queuing Protocol'' and Boot also provides
 auto-configuration options for `RabbitTemplate` and RabbitMQ.
 
+[[boot-features-messaging]]
+== Spring Integration
+
+Spring Integration provides abstractions over messaging and also other 
+transports such as HTTP, TCP etc. If Spring Integration is available
+on your classpath it will be initialized through the `@EnableIntegration`
+annotation. Message processing statistics will be published over JMX if
+``spring-integration-jmx'' is also on the classpath. 
+See the {sc-spring-boot-autoconfigure}/integration/IntegrationAutoConfiguration.{sc-ext}[`IntegrationAutoConfiguration`]
+class for more details.
+
 [[boot-features-jms]]
 == JMS
 
@@ -1792,6 +1803,17 @@ into your own beans:
 	}
 ----
 
+[[boot-features-jmx]]
+== Monitoring and management over JMX
+
+Java Management Extensions (JMX) provide a standard mechanism to
+monitor and manage applications. By default Spring Boot will create an
+`MBeanServer` with bean id "mbeanServer" and expose any of your beans
+that are annotated with Spring JMX annotations (`@ManagedResource`,
+`@ManagedAttribute`, `@ManagedOperation`).
+
+See the {sc-spring-boot-autoconfigure}/jmx/JmxAutoConfiguration.{sc-ext}[`JmxAutoConfiguration`]
+class for more details.
 
 [[boot-features-testing]]
 == Testing