darshan mmap file names may not always be unique
In cases where a job script issues multiple run commands (srun, aprun, etc), the generated mmap file names will be identical in each run, causing Darshan to fail for all runs except the first one.
We need to add another component to the log file name that can distinguish between each of these runs. Start time won't work as its entirely possible multiple sruns could start within the same second (especially parallel invocations).