Minimize randomly generated log names.

[blaze-developer]

Every time we go to download a log from the robot, we have to scroll past a mountain of random hash log file names. It would be useful if the files got renamed, and not just a new one was created, or if the old file is deleted after the new one is created. I think AdvantageKit already attempts to do this, but in our experience it has only created duplicate log files, not deleted randomly named ones.