Add dependency support for direct mbeans.

[WFLY-3921]; 
We should be able to depend on existing mbeans from jboss-service.xml.
(e.g. mbeans registered directly from JMX API)
I don't understand the need for this interface. There are 2 impls:

1) MscMBeanServer.  This implements registerMBeanInternal exactly the same as registerMBean, so the added method adds nothing.

2) PluggableMBeanServerImpl. The only thing registerMBeanInternal does is set a boolean var to true which then triggers calling registerMBeanInternal on the delegate. But the only delegate is MscMBeanServer which... see 1).