storage images: allow ImageDestination ID reuse
storage images: allow ImageDestination ID reuse

When committing an image, if an image already exists that's using the
same ID (most likely because the reference we used to generate the image
ID included one), reuse it if it uses the same top layer that we wanted
the new image to use.

Signed-off-by: Nalin Dahyabhai <f562fcb2a0b898bf0be1afc867ea92325d8f825f@redhat.com>

masters-of-cats/image,containers/image,containers/image