This commit sets the log of the internal transport client used in the
Elasitcsearch 5 binding to use standard error instead of standard out.

This commit adds some basic formatting to the transport client logs for
the transport client used in the Elasticsearch 5 binding.

This commit sets the Elasticsearch 5 binding to only use the
elasticsearch-maven-plugin if tests are running on JDK 8.

This commit updates the Elasticsearch 5 binding docs to include
references for starting Elasticsearch 5, how to configure the transport
client, and how to use the low-level REST client binding.

This commit fixes issues with the Elasticsearch 5 transport client and
REST client bindings so that all tests pass.

This commit is a straightforward code cleanup of the Elasticsearch 5
transport client and REST client implementations.

This commit is an initial cut at a complete implementation using the
low-level Elasticsearch REST client.

This commit fixes a bug in the Elasticsearch 5 transport client
binding. Namely, the update method was not indexing using the ID of the
read document, but instead the provided key. As auto-generated IDs are
used, this is a mistake as this is not the ID of the document. This
commit fixes this issue.

Additionally, the type is passed to the search method and used in
searches. While this is not a correctness issue per se, we fix it for
clarity.

We can remove the path.home setting for the Elasticsearch 5 binding for
the transport client so this commit does that.

This commit refactors the indexing of documents in the Elasticsearch 5
binding to use auto-generated IDs, instead indexing the key field as a
dedicated field rather than using it as the ID. This enables us to
implement scan functionality which we add in this commit as well.

Upstream Elasticsearch does not support embedded nodes as of
Elasticsearch 5. This commit removes the usage of embedded nodes within
YCSB.

Since Elasticsearch 5, Elasticsearch is now strict about settings. This
means that if you pass it a setting that it does not recognize,
Elasticsearch will throw an exception whereas previously it was lenient
in such situations. This commit removes passing all properties as
settings to Elasticsearch in favor of a special prefix es.setting for
which properties prefixed with this will be passed as settings to
Elasticsearch.

If path.home is not set we should not add it to the settings object used
to construct the transport client otherwise we will hit a null pointer
exception due to the null value being dereferenced in the internals of
Elasticsearch.

This commit bumps the Elasticsearch dependency version of the
Elasticsearch 5 binding to version 5.5.1.