Discovery hosts should be domains

Description

In elasticsearch.yml file there is entry discovery.seed_hosts: which have internal cluster addresses in it. We should add option to define and use replication domain there.

Why?

Becasuse when dns have more than one domain at the same address elasticsearch will wait for connection from fist domain which will be returned by dns and that could be not what user want.

Proposal

Add optional domain key to elasticsearch_endpoints variable.