Reconfigure fio unit test to avoid missing log warnings?

[webbnh]

Based on Dave's comment, it sounds like the mocking skips actually running the workload, which explains why no log history records are produced. So, should we be omitting the log_hist_msec (which should suppress the warnings), or are we happier getting and verifying the warnings?

Originally posted by @webbnh in #2636 (comment)