MEXICO CITY — Mexico’s most powerful drug cartels are recruiting former Colombian soldiers, prompting Mexican authorities to turn away dozens of Colombians trying to enter the country in recent weeks, Mexico’s security chief said Tuesday. Security Secretary Omar García Harfuch’s comments followed the arrest last week of 12 Colombians in the western state of Michoacan in connection with a mine attack that killed eight Mexican soldiers. Through contact with Colombian authorities, García Harfuch