Refer keytool using relative path

We will assume JDK bin/ is in the PATH, instead of using an absolute
path.

TEST=sign_official_image.sh
BUG=b:29915721,chrome-os-partner:56279

Change-Id: I55379a8409b7d81f213d4d7418133691fa8152cf
Reviewed-on: https://chromium-review.googlesource.com/373558
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Victor Hsieh <victorhsieh@chromium.org>
1 file changed