WASHINGTON – A retired four-star U.S. Navy admiral was sentenced on Tuesday to six years in prison for his conviction on corruption charges that he agreed to exchange a military contract for a lucrative postretirement job. Retired Adm. Robert P. Burke – once the second-highest uniformed officer in the Navy – was commanding its forces in Europe and Africa when he engaged in a bribery plot with two business executives, according to federal prosecutors. A jury convicted Burke of four counts,