ES REST client with Authentication & more

[mars]

I'm currently testing using your fork of the Universal Recommender with this PredictionIO 0.11.0 branch that enables basic HTTP authentication for Elasticsearch.

Just opening this pull request to share with you what we're doing, not trying to merge yet, and see if you're headed in the same direction. @dszeto pointed me to your fork.

Things we've done:

• upgrade to Scala 2.11 & Spark 2.1
• use a custom PredictionIO 0.11.0 SNAPSHOT for Authentication (this is in a local Maven repo)
• fixup JSON request bodies for index creation

To do:

• fix EsClient#hotSwap to work from an initial, empty state

Curious to know if any of this seems useful to you? Have you hit any issues with initial ES index creation?

Thanks for sharing your progress so far 😃