Launcher `log_location` attr does not handle directories

[Bubballoo3]

@harshit-soora noticed earlier this week that the log_location form item will fail if you pass a directory. I think the expected behavior is probably that it would create the same slurm-2715475.out automated filename in the specified directory. If this seems like something we want to implement that is probably the best solution, or we can add a note to OSC/ood-documentation#1242 to make sure we tell people how to use it.