Use msg_gerr() for error prints

This makes it so that prints which occur in error conditions are
directed to stderr.

BUG=chromium:369188
BRANCH=none
TEST=built for alex and nyan, ran a few invalid commands to make
sure error output only showed up if stderr is not sent to /dev/null

Change-Id: I2bade50e8a4025eced3055ddfd41837d68c159af
Reviewed-on: https://chromium-review.googlesource.com/198266
Reviewed-by: Yung-chieh Lo <yjlou@chromium.org>
Commit-Queue: David Hendricks <dhendrix@chromium.org>
Tested-by: David Hendricks <dhendrix@chromium.org>
1 file changed