build_image: log emerge commands

It helps to see the exact emerge command when installing packages
into the rootfs images.  This adds ~5 lines to build_image which
should be nothing.

BUG=None
TEST=`./build_image --board=kumo test` produces some nice log lines

Change-Id: I2c781d51d07bb48772528cbbb13b4eb80fde5712
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/1928571
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/build_library/build_image_util.sh b/build_library/build_image_util.sh
index 87547e3..3d142c9 100755
--- a/build_library/build_image_util.sh
+++ b/build_library/build_image_util.sh
@@ -194,8 +194,10 @@
 # Arguments to this command are passed as addition options/arguments
 # to the basic emerge command.
 emerge_to_image() {
-  sudo -E ${EMERGE_BOARD_CMD} --root-deps=rdeps --usepkgonly -v \
+  set -- ${EMERGE_BOARD_CMD} --root-deps=rdeps --usepkgonly -v \
     "$@" ${EMERGE_JOBS}
+  info "$*"
+  sudo -E "$@"
 }
 
 # Create the /etc/shadow file with all the right entries.