ISPN-3335 JMX statistics for Queries do not work after adding new classe...

...s to SearchFactory

In Infinispan we use SearchFactory reconfiguration when adding new classes. This process actually builds a new SearchFactory behind the scenes which should preserve all state and config of the old one, plus the new added classes. Unfortunatelly this does not work correctly due to https://hibernate.atlassian.net/browse/HSEARCH-1461. The statistics are lost on each reconfiguration. Also the the status of Statistics.isStatisticsEnabled is lost.  

This is worked around by constructing a new MBean statistics implementtion, with identical interface. The new implementation accumulates its own statistics counters and gathers current data from the current Statistics object of the SearchFactory.

Please integrate in master.

Jira: https://issues.jboss.org/browse/ISPN-3335