Make sure log events generated at shutdown phase of plugins (except

[mururu]

corresponding filter and output) are emitted

Here is an example. In this case, out-ok-1, in-ok, filter-ok and out-ok-2 should be captured. filter-ng and out-ng should not be captured because they match fluentd's event logs. Note that the captured logs appear twice due to stdout filter.

<match test>
  @type null
  @id out-ok-1
</match>

<source>
  @type dummy
  tag dummy
  @id in-ok
</source>

<filter test>
  @type stdout
  @id filter-ok
</filter>

<label @X>
  <match hoge>
    @type null
    @id out-ok-2
  </match>
</label>

<filter fluent.**>
  @type stdout
  @id filter-ng
</filter>

<match fluent.**>
  @type stdout
  @id out-ng
</match>

2017-07-12 19:25:28 +0900 [info]: shutting down fluentd
2017-07-12 19:25:28 +0900 [info]: shutting down input type="dummy" plugin_id="in-ok"
2017-07-12 19:25:29 +0900 fluent.info: {"message":"shutting down fluentd"}
2017-07-12 19:25:28 +0900 fluent.info: {"message":"shutting down fluentd"}
2017-07-12 19:25:29 +0900 fluent.info: {"type":"dummy","plugin_id":"in-ok","message":"shutting down input type=\"dummy\" plugin_id=\"in-ok\""}
2017-07-12 19:25:28 +0900 fluent.info: {"type":"dummy","plugin_id":"in-ok","message":"shutting down input type=\"dummy\" plugin_id=\"in-ok\""}
2017-07-12 19:25:29 +0900 [warn]: no patterns matched tag="dummy"
2017-07-12 19:25:29 +0900 [info]: shutting down output in @X type="null" plugin_id="out-ok-2"
2017-07-12 19:25:29 +0900 [info]: shutting down filter type="stdout" plugin_id="filter-ok"
2017-07-12 19:25:29 +0900 [info]: shutting down output type="null" plugin_id="out-ok-1"
2017-07-12 19:25:29 +0900 fluent.warn: {"tag":"dummy","message":"no patterns matched tag=\"dummy\""}
2017-07-12 19:25:29 +0900 fluent.warn: {"tag":"dummy","message":"no patterns matched tag=\"dummy\""}
2017-07-12 19:25:29 +0900 fluent.info: {"type":"null","plugin_id":"out-ok-2","message":"shutting down output in @X type=\"null\" plugin_id=\"out-ok-2\""}
2017-07-12 19:25:29 +0900 fluent.info: {"type":"null","plugin_id":"out-ok-2","message":"shutting down output in @X type=\"null\" plugin_id=\"out-ok-2\""}
2017-07-12 19:25:29 +0900 fluent.info: {"type":"stdout","plugin_id":"filter-ok","message":"shutting down filter type=\"stdout\" plugin_id=\"filter-ok\""}
2017-07-12 19:25:29 +0900 fluent.info: {"type":"stdout","plugin_id":"filter-ok","message":"shutting down filter type=\"stdout\" plugin_id=\"filter-ok\""}
2017-07-12 19:25:29 +0900 fluent.info: {"type":"null","plugin_id":"out-ok-1","message":"shutting down output type=\"null\" plugin_id=\"out-ok-1\""}
2017-07-12 19:25:29 +0900 fluent.info: {"type":"null","plugin_id":"out-ok-1","message":"shutting down output type=\"null\" plugin_id=\"out-ok-1\""}
2017-07-12 19:25:29 +0900 [info]: shutting down filter type="stdout" plugin_id="filter-ng"
2017-07-12 19:25:29 +0900 [info]: shutting down output type="stdout" plugin_id="out-ng"
2017-07-12 19:25:29 +0900 [info]: process finished code=0

[repeatedly]

LGTM