By Jack Kim SEOUL (Reuters) -North Korea tested its new submarine-launched cruise missiles (SLCM) on Sunday, firing an upgraded missile for the second time in a week and accelerating its navy’s nuclear armament, state media reported on Monday. Leader Kim Jong Un supervised the test of the missile, called “Pulhwasal-3-31,” which is identical to the strategic cruise missiles that the North test-launched last week as part of upgrading its weapons system. State news agency KCNA and official Rodong Sinmun newspaper said the missiles flew above the sea off the country’s east coast for 7,421 seconds …