After `MessagingAnnotationPostProcessor` fix for the late endpoints
registration we end up with the fact that `IntegrationMBeanExporter`
tries to register an `MBean` for the `MessageHandler/MessageSource`
one more time after parsing an `AbstractEndpoint`.
We don't fail because we catch an exception for already registered MBean
and just log it with ERROR
* Fix `IntegrationMBeanExporter` to check for
`MessageHandler/MessageSource` presence in the registered `objectNames`
* Some refactoring in the `IntegrationMBeanExporter` and fixes for
Sonar smells
9cf52b7281