Jenkins performance test runtimes

The performance tests are now run 5 times for each Jenkins result, with the results being averaged. That means the turnaround time for a single set of performance tests is around 5 hours.

I think it's worth reviewing how much benefit we get from running the tests 5 times each. IMO It would be better if we can stabilise the test configurations and run them a single time, rather than generating an average result.