remove Joi validation, add createClient, update tests

src/helpers/create_client.js

@@ -0,0 +1,13 @@
+import elasticsearch from 'elasticsearch';
+
+export default function createClient(options) {
+  let client;
+
+  if (options instanceof elasticsearch.Client) {
+    client = options;
+  } else {
+    client = new elasticsearch.Client(options);
+  }
+
+  return client;
+};