19165: Adds exist_ok=True to trace directory creation call

[cademack]

Adding exist_ok=True on the mkdir call that creates the directory for the tracefile.

We believe this may be the cause of some test failures where a race condition exists where multiple processes find the directory does not exist, then one creates the directory before the rest. This means that when the following processes attempt to create the directory, it already existed. Adding this flag should prevent these exceptions.