Chris Willman Senior Music Writer and Chief Music Critic One of the buzziest — or should that be tipsiest? — performances at this past weekend’s Stagecoach came from an artist who wasn’t even listed on the poster art. Late-breaking sensation Shaboozey was squeezed into the festival as a performer in the Bud Light Backyard tent, where there was other squeezing going on as Sunday’s festivalgoers stood in line to get a glimpse of the artist whose “A Bar Song (Tipsy)” has proven to be a straight-out-of-the-box smash among both country and hip-hop fans. Shaboozey isn’t coming to stardom himself in any kind of overnight way; the 28-year-old, Virginia-born singer-rapper put out his first single 10 years ago, and he’s about to release his third major-label album.