On paper, the job of starring in “Ponies” looks tricky. The lead roles are two young women working at the U.S. embassy in Moscow in the late 1970s. Their husbands die unexpectedly in a plane crash that might not have been an accident. As they’re in mourning, they’re unexpectedly drafted into undercover jobs for the CIA. The missions put them in harm’s way at every moment, forcing them to acquire espionage skills they don’t have or risk capture, …