The Napa Valley Opera House burnished its reputation for cultural diversity Friday night, presenting a rip-roaring night of country fiddling, field hollering and some mournful blues. The show, titled “Hills to Hollers,” featured three musical virtuosos – soul singer and drummer Linda Tillery, bluegrass singer and fiddler Laurie Lewis and multi-genre singer-fiddler-pianist Barbara Higbie – in a two-show of rousing musicality.