HK-Shenzhen stock link to start in days as China opens up markets more

* Shenzhen scheme to start in a few days: HKEX CEO * Shenzhen offers world's largest untapped opportunity: HSBC * Investment flows into HK from China may continue to outpace (Adds investor comments, Shenzhen market size) Nov 18 (Reuters) - A long-awaited stock trading link between Hong Kong and Shenzhen will go live in coming days, the CEO of Hong Kong's bourse said, further opening up China's capital markets to global investors and giving them access to some of its fastest growing companies. Wi