Gerard Butler is an actor who knows his strengths and takes roles that play to them, and his charismatic lead performance is one of the best things about “Kandahar,” a military action thriller about undercover CIA operative Tom (Gerard Butler) who is stuck deep in hostile territory in Afghanistan with his translator, Mo (Navid Negahban). It’s vaguely familiar to this year’s “The Covenant” from Guy Ritchie, yet the two films are very different. Here, the two men must work together to avoid the elite special forces unit that has been tasked with hunting them down after their mission is exposed. ...