Livermore Opera opens its La traviata with a known quantity, in Rebecca Davis, who has sung Violetta Valery at Opera San Jose and is an alumna of the Merola Opera Program. David Gustafson, her Alfredo, sang in the company’s La Boheme in November, and has had a notable career, locally. Torlef Borsting is more solid casting, as Germont, so this local company can take pride in delivering quality singers for this audience favorite.