Add search concurrency to geo benchmarks

[iverase]

We added search concurrency to lucene bench, let's add it as well; to the geo benchmarks. I added a new otional parameter called searchConcurrency that accepts an integer greater or equal to zero. This is how it works:

• if not added, the searches will be run with the number of threads defined by Runtime.getRuntime().availableProcessors();
• if zero, it runs with no search concurrency (like now)
• if a positive integer, this will the number of threads in the threadpool.

[iverase]

btw, it gives a very nice speed up for the queries I tested :)

[iverase]

Thanks for the quick review and merge! I think it is fine to do nothing an maximise concurrency for the benchmarks.