format in_tail path with the specified timezone

[tatsu-yam]

Which issue(s) this PR fixes:
None

What this PR does / why we need it:
If the file path which in_tail plugin reads includes strftime format, it is determined by system timezone.
I want to determine this path in the specified timezone for each tail plugin object.
For example, a fluentd process reads a UTC file path ( /path/to/data/test_utc/20191210_04.json ) and a JST file path ( /path/to/data/test_jst/20191210_13.json ) in one conf.

$ TZ='Asia/Tokyo' ./bin/fluentd -c test.conf
2019-12-10 13:48:19 +0900 [info]: parsing config file is succeeded path="test.conf"
2019-12-10 13:48:19 +0900 [info]: using configuration file: <ROOT>
  <source>
    @type tail
    path "/path/to/data/test_utc/%Y%m%d_%H.json"
    pos_file "/path/to/pos/test_utc.pos"
    tag "test_utc"
    timezone "+00"
    <parse>
      @type "json"
    </parse>
  </source>
  <source>
    @type tail
    path "/path/to/data/test_jst/%Y%m%d_%H.json"
    pos_file "/path/to/pos/test_jst.pos"
    tag "test_jst"
    <parse>
      @type "json"
    </parse>
  </source>
  <match **>
    @type stdout
  </match>
</ROOT>
2019-12-10 13:48:19 +0900 [info]: starting fluentd-1.7.4 pid=64544 ruby="2.5.5"
...
2019-12-10 13:48:20 +0900 [info]: #0 following tail of /path/to/data/test_jst/20191210_13.json
2019-12-10 13:48:20 +0900 [info]: #0 following tail of /path/to/data/test_utc/20191210_04.json

I wrote a simple path, but is it correct to use Fluent::Timezone class?

Docs Changes:
None

Release Note:
None

[ganmacs]

It's reasonable for me to use Fluent::Timezone for such purpose.

@repeatedly ?

[repeatedly]

Yes. Fluent::Timezone is better to handle timezone task.

[tatsu-yam]

Thank you for reply.
I'll continue as it is and remove "Draft" after adding the following:

• since option is only used to determine the path, change it from timezone to path_timezone or is there a better name?
• add the same implementation to exclude_path
• add test

If there are any problems, please point them out.

[ganmacs]

since option is only used to determine the path, change it from timezone to path_timezone or is there a better name?

Sounds good. I've thought same thing. path_timezone is better.

Could you follow the DCO https://github.com/fluent/fluentd/pull/2719/checks?check_run_id=341323383 ?(I think you know. it's just confirming)

[tatsu-yam]

Could you follow the DCO https://github.com/fluent/fluentd/pull/2719/checks?check_run_id=341323383 ?(I think you know. it's just confirming)

Sure, I'll squash commits and sign off at that time.

[cosmo0920]

[ganmacs]

Thank you!