image_signing: Fix the wrong output to VERSION.signer.
image_signing: Fix the wrong output to VERSION.signer.

The helper function - info redirects msg to stderr and appends some
backslash escapes so
  1. it can't be redirected to VERSION.signer via stdout again.
  2. Even if change to stderr, we also don't want these appended
     msg.

BUG=chromium:760879
TEST==~/trunk/src/platform/vboot_reference/scripts/image_signing/sign_official_build.sh
recovery ../build/images/coral/latest/recovery_image.bin
../platform/vboot_reference/tests/devkeys
BRANCH=None

Change-Id: I46d560fb4cb93756fd02e32412410afb3a4db0e2
Reviewed-on: https://chromium-review.googlesource.com/861694
Commit-Ready: Marco Chen <cddf73c2eeb445eb5022e73c23b1c49a27aefb07@chromium.org>
Tested-by: Marco Chen <cddf73c2eeb445eb5022e73c23b1c49a27aefb07@chromium.org>
Reviewed-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot