Avoiding failure when using frozen indices

[masseyke]

This commit changes es-hadoop to treat frozen indices as empty indices rather than throwing exceptions. Before
this change if you query a frozen index with es-hadoop or spark you get job failure with an exception like this:

org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 0.0 failed 4 times, most recent failure: Lost task 0.3 in stage 0.0 (TID 3) (localhost executor 2): org.elasticsearch.hadoop.EsHadoopIllegalArgumentException: invalid response
	at org.elasticsearch.hadoop.util.Assert.isTrue(Assert.java:60)
	at org.elasticsearch.hadoop.serialization.ScrollReader.read(ScrollReader.java:272)
	at org.elasticsearch.hadoop.serialization.ScrollReader.read(ScrollReader.java:263)
	at org.elasticsearch.hadoop.rest.RestRepository.scroll(RestRepository.java:313)
	at org.elasticsearch.hadoop.rest.ScrollQuery.hasNext(ScrollQuery.java:94)
	at org.elasticsearch.spark.rdd.AbstractEsRDDIterator.hasNext(AbstractEsRDDIterator.scala:66)
	at org.apache.spark.util.Utils$.getIteratorSize(Utils.scala:1889)
	at org.apache.spark.rdd.RDD.$anonfun$count$1(RDD.scala:1253)
	at org.apache.spark.rdd.RDD.$anonfun$count$1$adapted(RDD.scala:1253)
	at org.apache.spark.SparkContext.$anonfun$runJob$5(SparkContext.scala:2254)
	at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:90)
	at org.apache.spark.scheduler.Task.run(Task.scala:131)
	at org.apache.spark.executor.Executor$TaskRunner.$anonfun$run$3(Executor.scala:506)
	at org.apache.spark.util.Utils$.tryWithSafeFinally(Utils.scala:1462)
	at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:509)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

We don't want to change behavior to read frozen indices by default since they will be very slow. We might add some config to have es-hadoop pass in ignore-throttled so that frozen indices can be queried. But since they are deprecated that might not be worth the effort.
Relates #1734

[jbaiera]

LGTM