crash-reporter: disable device coredumps in verified mode

Device coredumps should only be available in developer mode.

BUG=None
TEST=link boot with devcoredump series

Signed-off-by: Kees Cook <keescook@chromium.org>
Change-Id: Ia86c32310887199b268b1f71221c6eb8a02f7827
Reviewed-on: https://chromium-review.googlesource.com/231386


Reviewed-by: Mike Frysinger <vapier@chromium.org>