* Nearly 400,000 people flee to storm shelters
* Storm verges on becoming a "supercyclone"; could affect 12 mln people
* Operations at key eastern port halted; major gas field seen spared
By Sruthi Gottipati and Jatindra Dash
ICHAPURAM/BHUBANESWAR, India, Oct 12 (Reuters) - Rain and wind lashed India's east coast and nearly 400,000 people fled to storm shelters after authorities issued ...