It was an absolute power play. A 12-year-old Long Island hockey player who lost his varsity star brother to a rare heart condition was given the day of a lifetime by the Islanders, as he skated to center ice ahead of Saturday’s 3-0 loss against the Senators . “I was really nervous at first,” Massapequa’s Cole Kasin admitted to The Post after fist-bumping Bo Horvat on the blue line during the national anthem. “Then I got out there, and it was crazy,” added the passionate little Isles fan with