[riak] New YCSB binding for Riak. The binding is based on the one created by Basho Technologies (available at https://github.com/basho-labs/YCSB/tree/master/riak). [riak] Made compatible with the latest YCSB version. [riak] Added strong consistency test support and made it default. [riak] Added missing results return based on provided fields in scan/read functions. [riak] Added TIME_OUT status return code for those transactions which take too long to complete. [riak] Added flexible test parameter specification via customizable configuration file and command line options support. [riak] Added test unit. [riak] Removed unused Constants.java file. [riak] Removed many unused function in the RiakUtils.java file. [riak] Choosed to use executeAsync methods to resolve a bug that didn't allow the benchmark to end whenever one or more nodes of the cluster are killed. [riak] Fixed license issues in all files. [riak] Done some refinements to the code.