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.