“The Law School Scam,” a 2014 investigative article in The Atlantic, was the inspiration for John Grisham’s latest novel, “The Rooster Bar.” Mr. Grisham’s tale is a thoroughly engaging, seriocomic caper that satirizes and exposes unsavory for-profit law schools, along with banks that exploit students with loans they’ll never be able to pay off, unfair United States immigration policies — and, for that matter, the entire legal profession in this country.