Add simple benchmark sbatch scripts

[dmargala]

This PR adds a few scripts that can be run with sbatch on nersc to perform simple benchmarks of the cpu version of the code.

[dmargala]

A couple things to consider before merging:

• print the diff of start and end time so don't have to do math later
• one line command to run benchmark suite
• timing within spex to ignore srun start up time
• change input file directory to point to andes

[dmargala]

I've added some logic in the job script to compute and print the time diff in seconds and do the conversion to "frames per node hour".

@sbailey, any other suggestions before merging?