ES bulk request entity too large while executing index operation

- Version: 0.5.1
- Storage Backend: HBase
- Mixed Index Backend: ElasticSearch 6.1.3
- Mailing list Thread URL:
- Steps to Reproduce: Executing a reindex job on mapreduce

### Stack Trace

```
2020-06-04 18:50:30,817 282383 [Thread-19] WARN org.apache.hadoop.mapred.LocalJobRunner - job_local112793509_0001
java.lang.Exception: org.janusgraph.core.JanusGraphException: Unknown exception while executing index operation
at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:522)
Caused by: org.janusgraph.core.JanusGraphException: Unknown exception while executing index operation
at org.janusgraph.graphdb.olap.job.IndexRepairJob.workerIterationEnd(IndexRepairJob.java:206)
at org.janusgraph.graphdb.olap.VertexJobConverter.workerIterationEnd(VertexJobConverter.java:118)
at org.janusgraph.hadoop.scan.HadoopScanMapper.cleanup(HadoopScanMapper.java:130)
at org.janusgraph.hadoop.scan.HadoopVertexScanMapper.cleanup(HadoopVertexScanMapper.java:55)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:149)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:787)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:243)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.janusgraph.diskstorage.PermanentBackendException: Unknown exception while executing index operation
at org.janusgraph.diskstorage.es.ElasticSearchIndex.convert(ElasticSearchIndex.java:447)
at org.janusgraph.diskstorage.es.ElasticSearchIndex.restore(ElasticSearchIndex.java:895)
at org.janusgraph.diskstorage.indexing.IndexTransaction.restore(IndexTransaction.java:128)
at org.janusgraph.graphdb.olap.job.IndexRepairJob.workerIterationEnd(IndexRepairJob.java:201)
... 12 more
Caused by: org.elasticsearch.client.ResponseException: method [POST], host [http://10.1.***.***:9200], URI [/_bulk], status line [HTTP/1.1 413 Request Entity Too Large]

at org.elasticsearch.client.RestClient.convertResponse(RestClient.java:283)
at org.elasticsearch.client.RestClient.performRequest(RestClient.java:261)
at org.elasticsearch.client.RestClient.performRequest(RestClient.java:235)
at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.performRequest(RestElasticSearchClient.java:483)
at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.performRequest(RestElasticSearchClient.java:474)
at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.bulkRequest(RestElasticSearchClient.java:397)
at org.janusgraph.diskstorage.es.ElasticSearchIndex.restore(ElasticSearchIndex.java:893)
... 14 more
```

Start with ElasticSearchIndex.restore and convert, then follow the call into RestElasticSearchClient.bulkRequest shown in the stack trace. Reproduce the mapreduce reindex job against Elasticsearch 6.1.3 and inspect the bulk request failure; done means the index operation no longer fails with HTTP 413 Request Entity Too Large.

Written by the indexing model from the issue text.