Randomize execution order of benchmarks

[smarr]

To avoid systematic bias that might be caused by operating system caches or hardware/memory properties, the execution order of benchmark runs should be randomized.

This has the additional benefit of producing data points for more benchmarks and it is possible to see trends of the results earlier for long running sets of benchmarks.

There needs to be an option to suppress the randomization, of course.
Also, we should have an estimate of what that means in terms of memory usage when many microbenchmarks are executed (need to keep the data in memory to calculated confidence interval, etc...)

[smarr]

I think this has already been implemented, and is supported with:

  -s SCHEDULER, --scheduler=SCHEDULER
                        execution order of benchmarks: batch, round-robin,
                        random [default: batch]