Remove hostname field as Hostname is preferred

For openstack.** tagged, the additional hostname field is added,
while we already got Hostname (case sensitive). In this case we should
drop hostname field, as these are redundant.

Change-Id: Id1ff2030c6ac6618b6d5fbe32ae3ed8ba861e27c
Partial-Bug: PROD-18295
diff --git a/fluentd/label/default_output/elasticsearch.yml b/fluentd/label/default_output/elasticsearch.yml
index 84b2dc1..8fc8958 100644
--- a/fluentd/label/default_output/elasticsearch.yml
+++ b/fluentd/label/default_output/elasticsearch.yml
@@ -22,6 +22,11 @@
                     value: ${fluentd:dollar}{if record.has_key?("context"); record["context"].delete("auth_token"); end; nil}
                   - name: _dummy_3
                     value: ${fluentd:dollar}{if record.has_key?("context"); record["context"].delete("auth_token_info"); end; nil}
+              drop_hostname_field:
+                tag: "openstack.**"
+                type: record_transformer
+                enable_ruby: true
+                remove_keys: '["hostname"]'
             match:
               elasticsearch_output:
                 host: ${_param:fluentd_elasticsearch_host}