Thread Pool: Update default settings (move from default cached to fixed)

[kimchy]

The default thread pool settings for most thread pools is problematic in it being cached (for example, for index, search) since its unbounded in its thread creations. Change the default thread pool settings to follows:

• index: type: fixed, size: num_proc
• bulk: type: fixed, size: num_proc
• get: type: fixed, size: num_proc
• search: type: fixed, size: num_proc * 2, queue_size: 1000
• percolate: type: fixed, size: num_proc
• management: type: scaling, size: 5
• flush: type: scaling, size: halfProcMax5
• merge : type: scaling, size: halfProcMax5,
• refresh: type: scaling, size: halfProcMax10
• warmer: type: scaling, size: halfProcMax5