Switching default relay to r.ext, for -dev only.

Change-Id: Id31dc4b170137165bece37fdd1cac4862daff38f
BUG: chromium:365928
TEST: manual
Reviewed-on: https://chromium-review.googlesource.com/196386
Reviewed-by: Robert Ginda <rginda@chromium.org>
Tested-by: Robert Ginda <rginda@chromium.org>