Users can specify the MBeanServer implementation in which to register the
MBeans by setting the org.apache.wicket.mbean.server.agentid property to
the agent id of the MBeanServer implementation they want, or by setting
org.apache.wicket.mbean.server.class to the mbean server class they want
(if both are provided, and the agent id returns a server, that one is used).
This initializer will log an error when no mbean server with the provided
agent id can be found, and will then fall back to use the platform mbean
server.