make_factory_toolkit: Set host_based flag to boolean type

Instead of defining it as a string, we should use DEFINE_boolean.

BUG=none
TEST=Run the script with and without --host_based. Check the resulting
toolkit shellball.

Change-Id: Ib6a737215b9ab21f3f3e3976db5f9c6622cdbb01
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/211252
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed