support elasticsearch2.0 & support plugin

[penfree]

1. elasticsearch 2.0 has already released， do you have plan to update to elasticsearch 2.0.
2. how to add plugin in the embed es node， could you make an easy-to-use interface for adding plugin and maybe plugin config files

[drewdahlke]

Hey @penfree

1. Elasticsearch does an awesome job being backwards compatible on indexes built with older versions. We'll typically upgrade our ES cluster first, make sure we're happy with it, and then loop back to upgrade the version we use in elasticsearch-lambda for rebuilding in hadoop to match. I haven't tried restoring 1.x generated snapshots into a 2.0 cluster specifically yet, but there's a good chance it'll just work. I do intend on creating a 2.0 branch in a couple months if someone doesn't beat me to it.

2. Elasticsearch in this project has been configured to load in plugins found on the classpath. I'm using the elasticsearch-phone plugin with elasticsearch-lambda and including it in the pom as a dependency is all that was required.