Retail medical clinics — you know, those little offices in places like Walmart that promise to treat minor ailments in the amount of time it takes to check out on the express line — have been around for a few years, but haven’t exactly won over tons of customers from the neighborhood GP. Now, it looks like they’re about to take off in a big way. Or collapse. Or do nothing. That’s what happens when you get a second opinion about the fact that Kroger is closing 20 of its Little Clinic branches.