By Hyonhee Shin SEOUL (Reuters) -North Korea has conducted a test of its underwater nuclear weapons system in a protest against this week’s joint military drills by South Korea, the United States and Japan, state media KCNA said on Friday. The test of the “Haeil-5-23” system, a name North Korea has given to its nuclear-capable underwater attack drones, was carried out by the defence ministry’s think tank in the waters off its east coast, the report said, without specifying a date. The ministry’s unnamed spokesman accused the United States, South Korea and Japan of “getting frantic” with milita…