RFE: kola should log debug output (--debug) to a file

[ajeddeloh]

We don't want this in the console output in jenkins (because it's obnoxious to read) but it would be nice to log it to a file instead that can be included in _kola_temp.

[arithx]

I think we'd probably have to make it as an enhancement to capnslog if we want to keep outputting the non-debug output to stdout.

[euank]

Switching away from capnslog is also an option; There's been discussion in the past about migrating away coreos/pkg#57 (comment)

There are other libraries (like seelog) which natively have file output at various levels. It's more awkward with logrus (I think you add a Hook that handles file output?).

[arithx]

Found an example of using a Hook in logrus to output to multiple locations depending on error level: https://gist.github.com/cirocosta/0ca74af1d9700aad5ec40425ef587640