“You do not want to get stopped in Nashville with me in the car,” hard-rockin’ daddy Steve Earle warns a driver in his new tour film, Just an American Boy. Turns out Music City is also the home of the Fraternal Order of Police, and Earle, among other things, is a crusader against the death penalty, the author of “John Walker’s Blues,” and a felon whose firearm discharged twice into a crowd of cops during his arrest in a drug sweep. Director Amos Poe doesn’t make enough of this: There’s a tantalizing excerpt from Earle’s performance of “John Walker” on Fox News, but otherwise we mostly see him working his broad catalog (and a cover of “[What’s So Funny ‘Bout] Peace, Love & Understanding” that would have been fine in any other year) for adoring crowds. Looking puffier than he did in New York last month, Earle gets his band together, rewrites his play about executed Christian Karla Faye Tucker on the eve of opening night, defends his patriotism (and yours), and flogs the current LP. And then he rocks some more.