Timeout exception in direct index query.

Sometimes direct index query throws `TimeoutException`.
There is also similar problem with detailed explanation https://github.com/elastic/elasticsearch/issues/24069

```
Caused by: org.janusgraph.core.JanusGraphException: Could not execute operation due to backend exception
at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:57)
at org.janusgraph.diskstorage.BackendTransaction.executeRead(BackendTransaction.java:470)
at org.janusgraph.diskstorage.BackendTransaction.totals(BackendTransaction.java:464)
at org.janusgraph.graphdb.database.IndexSerializer.executeTotals(IndexSerializer.java:663)
at org.janusgraph.graphdb.query.graph.IndexQueryBuilder.executeTotals(IndexQueryBuilder.java:199)
at org.janusgraph.graphdb.query.graph.IndexQueryBuilder.edgeTotals(IndexQueryBuilder.java:244)
...
... 8 more
Caused by: org.janusgraph.diskstorage.PermanentBackendException: Permanent exception while executing backend operation Totals
at org.janusgraph.diskstorage.util.BackendOperation.executeDirect(BackendOperation.java:82)
at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:55)
... 22 more
Caused by: java.lang.RuntimeException: error while performing request
at org.elasticsearch.client.RestClient$SyncResponseListener.get(RestClient.java:681)
at org.elasticsearch.client.RestClient.performRequest(RestClient.java:219)
at org.elasticsearch.client.RestClient.performRequest(RestClient.java:191)
at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.performRequest(RestElasticSearchClient.java:320)
at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.search(RestElasticSearchClient.java:276)
at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.search(RestElasticSearchClient.java:53)
at org.janusgraph.diskstorage.es.ElasticSearchIndex.runCommonQuery(ElasticSearchIndex.java:974)
at org.janusgraph.diskstorage.es.ElasticSearchIndex.totals(ElasticSearchIndex.java:993)
at org.janusgraph.diskstorage.indexing.IndexTransaction.totals(IndexTransaction.java:129)
at org.janusgraph.diskstorage.BackendTransaction$TotalsCallable.call(BackendTransaction.java:453)
at org.janusgraph.diskstorage.BackendTransaction$TotalsCallable.call(BackendTransaction.java:442)
at org.janusgraph.diskstorage.util.BackendOperation.executeDirect(BackendOperation.java:69)
... 23 more
Caused by: java.util.concurrent.TimeoutException
at org.apache.http.nio.pool.AbstractNIOConnPool.processPendingRequest(AbstractNIOConnPool.java:364)
at org.apache.http.nio.pool.AbstractNIOConnPool.processNextPendingRequest(AbstractNIOConnPool.java:344)
at org.apache.http.nio.pool.AbstractNIOConnPool.release(AbstractNIOConnPool.java:318)
at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.releaseConnection(PoolingNHttpClientConnectionManager.java:303)
at org.apache.http.impl.nio.client.AbstractClientExchangeHandler.releaseConnection(AbstractClientExchangeHandler.java:239)
at org.apache.http.impl.nio.client.MainClientExec.responseCompleted(MainClientExec.java:387)
at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.responseCompleted(DefaultClientExchangeHandlerImpl.java:168)
at org.apache.http.nio.protocol.HttpAsyncRequestExecutor.processResponse(HttpAsyncRequestExecutor.java:436)
at org.apache.http.nio.protocol.HttpAsyncRequestExecutor.inputReady(HttpAsyncRequestExecutor.java:326)
at org.apache.http.impl.nio.DefaultNHttpClientConnection.consumeInput(DefaultNHttpClientConnection.java:265)
at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:81)
at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:39)
at org.apache.http.impl.nio.reactor.AbstractIODispatch.inputReady(AbstractIODispatch.java:114)
at org.apache.http.impl.nio.reactor.BaseIOReactor.readable(BaseIOReactor.java:162)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvent(AbstractIOReactor.java:337)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvents(AbstractIOReactor.java:315)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.execute(AbstractIOReactor.java:276)
at org.apache.http.impl.nio.reactor.BaseIOReactor.execute(BaseIOReactor.java:104)
at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$Worker.run(AbstractMultiworkerIOReactor.java:588)
at java.lang.Thread.run(Thread.java:748)
```

Start with the stack trace at IndexQueryBuilder.executeTotals and follow the call path through IndexSerializer, BackendTransaction, and ElasticSearchIndex.runCommonQuery. Compare the behavior with the linked Elasticsearch issue and investigate the RestElasticSearchClient request path. Done means the direct index query no longer intermittently fails with the reported TimeoutException, with regression coverage or a confirmed reproduction result.

Written by the indexing model from the issue text.