Switch how InSitu benchmark iterates

Previous version had a hard-coded loop for updating the dataset. This change relenquishes control over to google benchmarks. Running it from the command-line will iterate each sub-benchmark a different number of iterations depending on how long each individual test takes. The number of iterations can be increased (but not controlled) by increasing the minimum time for each test. Alternatively, using the "repetitions" argument, you can control exactly how many times the benchamrks are run.