Added new binding for Riak, based on the one created by Basho Technologies (available at https://github.com/basho-labs/YCSB/tree/master/riak).

Change made to the original version:

- Made compatible with the latest YCSB version.
- Removed unused Constants.java file.
- Added strong consistency test support.
- Done some refinements to the code.
- Removed many unused function in the RiakUtils.java file.
- 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.
- Added TIME_OUT status return code.

To do:
- Add different LOG errors (i.e. insufficient_vnodes_available, ring_not_ready, etc.) - for references, check page http://docs.basho.com/riak/latest/ops/running/recovery/errors/#Errors-and-Messages
- ...

Update cassandra2-cql driver to only run tests on jdk8

[cassandra] properly clear cached containers.

clear containers before we use them rather than after, so that in the case of
exceptions we can recover.

closes #127

[S3] Close opened S3Object

[hbase10] Fix the init() method to properly construct a single…

object. Previously N objects were instantiated because the method didn't
check to see if the connection was null.

[core] Add a UnixEpochTimestampGenerator

[dynamodb] Checkstyle updates for DynamoDB.

[geode] Checkstyle updates for Apache Geode (incubating)

[tarantool] Checkstyle updates for the Tarantool binding.

[infinispan] Checkstyle updates for the Infinispan binding.

[core] Add byte to double and long conversion methods to Utils.

These will be used for #653 to write timestamps and numeric values
to the ByteIterator maps.

Fixes #612.

S3Object opened in getS3ObjectAndMetadata() should be closed.

[hypertable] Checkstyle updates for the Hypertable binding.

Elasticsearch cleanup and version bump to 2.2.0

This commit fixes the Elasticsearch name in the README file for the
Elasticsearch project from "ElasticSearch" to "Elasticsearch".

This commit bumps the Elasticsearch dependency version from 2.1.1 to
2.2.0.

This commit fixes the Elasticsearch name throughout the YCSB benchmark
project from "ElasticSearch" to "Elasticsearch".

[core] added real version printout

Fixes #320

Updated top level README for YCSB 0.7.0 release

[couchbase] nit fix in Couchbase README

[orientdb] fixed scan with readallfields

[accumulo] don't run Accumulo tests on windows build.