OUAGADOUGOU, Burkina Faso — Heavy gunfire rang out at a military base in Burkina Faso’s capital early Sunday, prompting fears that a coup attempt was underway after weeks of growing frustration with the government’s handling of the Islamic insurgency wracking the West African country. The mutinous solders seized control of the Lamizana Sangoule military barracks in Ouagadougou, the capital.