images/build_images.py: support ALL

The docs and build_images.py claims to support ALL but it doesn't
actually work.  This change makes it work.

BUG=None
BRANCH=None
TEST=Verified that "make" now actually works rather than fails.

Change-Id: Ia2163742b98ce6b435135fe2e8228c5806f4f7d1
Signed-off-by: Matt Delco <delco@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1508972
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
1 file changed