Redirect Runner's stderr properly to Logger
Redirect Runner's stderr properly to Logger

`nuvolaplayer3 -L log.txt` is supposed to log all messages to the file
log.txt, but subprocess messages used to leak to stderr.

Issue: tiliado/nuvolaplayer#178

Signed-off-by: Jiří Janoušek <2a48236b6dcae98c8c0e90f4673742773ee17d91@gmail.com>

tiliado/nuvolaruntime,tiliado/nuvolaruntime,tiliado/nuvolaruntime,tiliado/nuvolaruntime