Support multi datacenter

Although http://janusgraph.org said that 'Multi-datacenter high availability and hot backups', it seems that janusgraph does not really support multi datacenter due to the fact that indexing background (solr/elasticsearch) dose not support multi-master replication cross multi datacenter (Solr 6 support master-slave replication).

And, below two questions are not answered completely:

1. Will JanusGraph work in multiple datacenters? 2017.11
https://groups.google.com/forum/#!topic/janusgraph-users/Tv_jeRdineQ

2. Are JanusGraph instances talking to each other when vertex ids are generated? 2017.12
https://groups.google.com/forum/#!searchin/janusgraph-users/datacenter/janusgraph-users/Y1IeC3NvocU/ZOWMpEqrCAAJ

So, will janusgraph provide a solution for multi-datacenter?

Start with the two linked JanusGraph user discussions and the issue's concern about Solr and Elasticsearch replication across datacenters. No repository file, test, or entry point is named; done would require a clearly defined, technically validated multi-datacenter solution or an explicit statement of supported limitations.

Written by the indexing model from the issue text.