Minor Description
This patch adds JMX capability to get statistics from all the SolrInfoMBean.
The implementation is done such a way to minimize code changes.
In SolrInfoRegistry, I have overloaded Map's put and remove methods to register and unregister SolrInfoMBean in MBeanServer.
Later on, I am planning to use register and unregister methods in SolrInfoRegistry and removing getRegistry() method (Hiding the map instance to other classes)