It shouldn’t come as a surprise that Bruce Hornsby’s music keeps being re-cool-ified. Hornsby is the very exemplar of dad-rock: 99 percent of the young population has been blasted with the piano man’s work on a family road trip at some point. So it stands to reason that Tupac should have a mellow moment sampling “That’s Just the Way It Is” and that, more recently, indie-rock mountain man Justin Vernon would invite Hornsby to perform the album of the same name at his music fest, Eaux Claires. But Hornsby is no one-trick pony. He has also made bluegrass records, gigged with a jazz band and even toured as part of the Grateful Dead. He and his band take the stage behind a rootsy new effort, Rehab Reunion.