CALISTOGA — Mike Bock casts his eyes downward as he recalls a fellow electric lineman who died a few years back. In his 29 years as a lineman with PG&E, he’s known four or five linemen who died in the line of work. Theirs is a job that doesn’t get a lot of notice. But on Saturday, a new movie, “Life on the Line,” starring John Travolta as a lineman, will premiere at 5 p.m. at the Lincoln Theater in Yountville during the Napa Valley Film Festival.