Bug 1446: Add JMX stats for clustered data store

  Added stats, available via JMX, to track data for the various
  thread pool executors used by the clustered data store.

Change-Id: Ifb8996075253e87b7fd4e7cb6cf876c3af80ff2a
Signed-off-by: tpantelis <tpanteli@brocade.com>
Merge "Bug 1446: Add JMX stats for clustered data store"