David Ortiz, Boston’s beloved slugger, has agreed to a contract extension that guarantees him $16 million for one year, 2015, and could keep him with the Red Sox through 2017. The sides agreed to terms shortly after Sunday’s exhibition game between the Red Sox and the Rays, and the Red Sox announced the completion of the deal late Sunday night. The deal includes a vesting club option for 2016 based on an undisclosed amount of plate appearances in ’15 and a club option for ’17.