Use new IOThreadPoolExecutor constructor to disable dynamic resizing
Use new IOThreadPoolExecutor constructor to disable dynamic resizing

Summary: As above

Reviewed By: disylh

Differential Revision: D23585845

fbshipit-source-id: 41a2c1c958b56fcb1fe73e86f127c85aa0337f2c

facebook/mcrouter,facebook/mcrouter,facebook/mcrouter,facebook/mcrouter