Java driver benchmarks

[Bouncheck]

Adds 3 separate java-driver benchmarks.

Java-driver-3.x and java-driver-4.x benchmarks were inspired by gocql and cpp implementations.
They use multiple threads with blocking execute calls. The intent was to make them similar enough to other implementations thus more comparable with them.

Java-driver-3.x-async runs config.concurrency many Futures that will chain with itselves using callbacks until all config.tasks request will be sent. Tasks are split evenly except for last <division remainder> tasks which are additionally assigned to single future.

Fixes #8.

[cvybhu]

Thank you for the contribution!

@avelanarius you're the most familiar with java driver, could you review when you get a moment?

[Bouncheck]

I've modified 3.x-async version according to reviews and updated PR message.