ref: d4f09d9048f5d7388358d3838fe02c5377cb79b9
parent: 52d25f544a9b5d6d47a64dee8fa3867d43ede287
author: sijchen <sijchen@cisco.com>
date: Mon Feb 29 06:40:25 EST 2016
put CWelsThreadPool to singleTon for future usage (including add sink for IWelsTask)