JIRA: https://jira.spring.io/browse/INT-3869
When using `@EnableIntegrationMBeanExport` with no `server` property,
the `IntegrationMBeanExportConfiguration` incorrectly created a new
`MBeanServer` instead of attempting to locate an existing one.
Use the `SpecificPlatform` logic from `MBeanExportConfiguration` to locate
a specific server on `WebSphere` and `WebLogic`; otherwise defer to
`JmxUtils.locateMBeanServer()` in the exporter's initialization method.
Add a test to verify the same server is used in multiple contexts.
* Fix `ConnectionFactoryTests` regarding new `MessageProducerSupport` logic
d8ad38d8ea