A mounting conflict in Libya is threatening to upset the global supply of oil at a time when prices are booming, and increases the likelihood that the U.S. will renew waivers for some buyers of Iranian oil, a U.S. official involved in the sanctions program said. Details of the Trump administration’s thinking come as a rogue general is mounting an offensive to take over the Libyan capital, potentially jeopardizing the country’s oil output recovery after a long production lull. …