By Jack Kim SEOUL (Reuters) - South Korean President Park Geun-hye rejected the resignation of her prime minister on Thursday and asked him to stay on after her second nominee for the job stood aside over controversial comments he had made about Korea's troubled past with Japan. The decision to keep incumbent Prime Minister Chung Hong-won, who tendered his resignation two months ago over the government's flawed response to a ferry disaster, heightened concerns about her ability to rule and push through reforms.