test: Make TEST_EQ print either 'comment' or 'desc'

Currently, test macros print out 'desc' regardless 'comment' is specified
or not. This patch makes TEST_EQ print 'desc' only if 'comment' is not
supplied.

BUG=none
BRANCH=none
TEST=make runtests

Change-Id: I9cc3c9a9561534352ae0315dfea983f2c212b909
Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/388859
Reviewed-by: Randall Spangler <rspangler@chromium.org>