Find worker logs in worker-artifacts subdirectory

[tdhopper]

STORM-901 moves worker log files into subdirectories which sparse tail doesn't find. This is an attempt to resolve that.

Closes #268, I think.

[coveralls]

Coverage remained the same at 45.417% when pulling b0b463c on tdhopper:tail_command into f66794f on Parsely:master.

[dan-blanchard]

Well, look who's back to making streamparse contributions. Thanks for the PR! 😄

Do you find yourself still using sparse tail with 1.0? We're not on it yet, but I know Storm UI now has log search builtin with it, and if you don't set your log path in config.json, all of your logs will automatically go in the Storm worker logs where they'll be searchable.

[tdhopper]

@dan-blanchard: We were just talking about that today. I haven't used it in the UI yet. I've been tailing logs manually by syncing input across tmux windows :)