Port collisions when using chrome headless

Because of the way that backstop is increment the debug port number on chrome, I will occasionally see failures with a Chromy error and no explanation. I finally figured it out, because the failures always happened after the same number of test cases, regardless of which tests I was running. One of the port numbers that Chromy attempts to use for the chrome-headless port is utilized, and then it causes a failure. Not sure what the solution should be, but it definitely happens where the port collision isn't handled well.