buffet: Add --log_to_stderr option Useful for debugging. Privetd and Peerd has the same. BUG=none TEST=sudo -u buffet buffet --log_to_stderr Change-Id: Ic60f6fcbc43087731f4e7343a04be5602af07212 Reviewed-on: https://chromium-review.googlesource.com/260300 Reviewed-by: Alex Vakulenko <avakulenko@chromium.org> Tested-by: Vitaly Buka <vitalybuka@chromium.org> Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>