When adding a reference to a manifest list or image index, if we are
guessing that it's a reference to an image in a registry, check if we
can read something from that location instead of assuming it's correct,
and if we can't, check for a local image.  This will let use use local
image IDs to refer to items that we want to add to a list or index.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>