[Tests] Elasticsearch: Remove the rescue so we can see what errors we get

`@es.indices.delete(:index => "*")` will not fail if there are no indices

See

```
~/ws/logstash (master)$ curl localhost:9200/_cat/indices
~/ws/logstash (master)$ curl -XDELETE localhost:9200/*
{"acknowledged":true}
```

it will only fail if we have a genuine issue like `{"error":"ElasticsearchIllegalArgumentException[Wildcard expressions or all indices are not allowed]","status":400}` which would be good to surface than just failing the test.