Supported versions are encapsulated in a new enum, ElasticVersion, that
provides a method to translate from the version string returned by the
Elasticsearch server.
Translation of the version works on prefix matching, with granularity
at the X.Y level. For example the version strings "2.4.0" and "2.4.6"
will both resolve to the V2_4 enum value.
This assumes that Elasticsearch has backwards compatibility between all
minor versions in the X.Y series, i.e. "2.4.0" and "2.4.6" should both
be equally compatible. If this turns out to not be the case, further
support can be added later.
ElasticVersionManager is renamed to ElasticIndexVersionManager to avoid
confusion with the ElasticVersion enum.
Change-Id: I4dfe443f0e5d26652433334cef6be8c2727e9317
90db6de2e0