HONG KONG (Reuters) - Luggage maker Samsonite International SA posted a 16.6 percent growth in first-half net sales, helped by strong performance of its high-end Tumi brand, sending its shares up 8.5 percent on Thursday.The world's largest luggage firm said global trading conditions in 2018 have so far been favourable, and the travel and tourism market continues to enjoy robust growth."We aim to sustain this momentum as we head into the remainder of the year," Chief Executive Officer Kyle..