James Bond might like a shaken, not stirred, martini, but Pierce Brosnan will take a mojito, please. At opening night of the Hamptons Film Festival at Gurney’s in Montauk, where Brosnan promoted his new movie, “The Greatest,” co-starring Susan Sarandon, the charming Irishman returned to the bar several times for refills of what he called “the best mojito ever made.” Also out east this weekend for the festival are Sharon Stone, Steve Buscemi, Alec Baldwin and Alan Alda.