[elasticsearch] Elasticsearch improvements

This commit fixes an issue with the index creation logic when the
elasticsearch.newdb flag is set to true. Namely, when running in local
mode the index would never exist (since the node always starts with a
clean temporary directory) but with elasticsearch.newdb an attempt would
be made to delete the index which would cause the workload to fail.

This commit also does a cleanup of the index creation logic using an
explicit create index request and passing the index settings along as
part of that index creation.

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.