For a classical percussionist, news of openings at the Boston Symphony Orchestra spur a frantic attempt. “Tetreault says he spent almost a year preparing for the audition. This was his life during that period: After working a full day of patchwork gigs scattered across Colorado, he’d go to his practice space until about 1 a.m., then drive home and be asleep by 2 a.m. And then at 6 o’clock, he’d get up and start all over again.”