Hongkonger Dr Lam Kwing-tong and his wife Lau So-kuen have not left their room on board the Diamond Princess cruise ship for more than a week, and are too scared to step out of it. And the closest the couple get to contact with the outside world is lingering on the private balcony of their stateroomBecause the ship, moored in Tokyo Bay, has become the largest single cluster of the deadly coronavirus outside mainland China.Lam, a dentist in Hong Kong, is concerned about the way crew serve food…