Add XPack authentication support

[srilumpa]

The elastic4play framework does not currently support authentication enabled on the ElasticSearch database enabled through the XPack component (cf TheHive-Project/TheHive#384).

Hopefully, this PR should add the feature. Setting the search.username (at least) and the search.password configuration directives will trigger the use of the XPack client. Otherwise, the current TCP client is used.

Unfortunately, I am not in position to test it thoroughly but executing sbt clean compile ends successfully and executing sbt test throws the same errors as the master branch.

Please let me know if this doesn't match your standards.

[nadouani]

@srilumpa This looks working fine for me. I've just tested it by installing x-pack plugin and setting a username/password couple.

If TheHive is not enabled to authenticate agains X-Pack, The "Elasticsearch cluster is unreachable" error is thrown, otherwise everything is OK.

Is this what we should expect?

I'll let @To-om merge it, since he knows more than me what's the next version to be released.

[srilumpa]

This is the error currently thrown when attempting to connect to a cluster with the X-Pack plugin enabled, so I guess keeping this when no credentials are set is OK.

I am not familiar enough with how you handle errors in the elastic4play framework and familiar enough with Scala in general to handle properly the exceptions but I can try something if you want to.

[nadouani]

It looks like the errors are handled at https://github.com/CERT-BDF/elastic4play/blob/master/app/org/elastic4play/ErrorHandler.scala, and we could probably add a pattern for org.elasticsearch.ElasticsearchSecurityException to customize the error message ;)