In shade, we use both md5 and sha256 checksums to help validate the
integrity of an image. Rather then having nodepool do this each time
for every time, have diskimage-builder create these files when we
build the image.
We've added a flag (disabled by default) to toggle this functionality.
Change-Id: I5815ba69b7d477f1e91dc8ec0c69c86168770964
Signed-off-by: Paul Belanger <pabelanger@redhat.com>