The checkpoint thread gets the current time-of-day, but does nothing
with it -- remove the retrieval.
Remove unused ms calculation.
lint: typo, parenthesis in the wrong place
If we start a monitor thread and populate, but never execute a workload,
we have a thread running but never set g_stop, so we hang.

Don't bother closing sessions on error, it makes some of the error handling
a little simpler.