Migrate out_exec_filter to v0.14 API

[cosmo0920]

I've tried to migrate out_exec_filter to v0.14 API.
Should we provide asynchronous buffered mode in this plugin?

[tagomoris]

I don't think so > async
Because writing data into pipes is atomic operation, and there are no way to confirm whether it succeeded or not.

[cosmo0920]

I don't think so > async
Because writing data into pipes is atomic operation, and there are no way to confirm whether it succeeded or not.

I see.

[tagomoris]

I missed to comment on this change: can you use child_process plugin helper for external process?

[tagomoris]

Hmm, I found there are some difficult points with child_process plugin helper. So I'll add following fixes for it.

[cosmo0920]

some difficult points

I've found that several difficult points for now:

• child_process helper does not have a functionality to distribute output into number of N processes
• child_process helper does not have a functionality to handle resident processes

[tagomoris]

#1297 does what this pull-request did. Let me close this now.