Update --prepackaged_autotest to --autotest_dir

BUG=None
TEST=Ran it

Change-Id: I63f8c351a974f988ae06af931d201bab97e467af
Reviewed-on: https://gerrit.chromium.org/gerrit/23423
Reviewed-by: Kris Rambish <krisr@chromium.org>
Tested-by: Kris Rambish <krisr@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Kris Rambish <krisr@chromium.org>
1 file changed