Create a ProbeHandler for JGroups

Expose the remote thread pool status to JGroups' probe. It returns the following:

• current-pool-size => the current pool size
• keep-alive=60000 => the configure keep alive time in milliseconds
• min-thread => the minimum thread pool size configured
• active-thread => the current active number of threads
• queue-size => the current queue size
• max-thread => the maximum thread pool size configured
• largest-pool-size => the largest thread pool