`crane rebase` now inspects the original image for annotations to
identify its old base and new base images. If those are found, and
--old_base and --new_base flags aren't specified, those will be used.

If the --rebased flag is not passed, the rebased image will be the
tagged with the original image reference; if it was originally specified
by digest, the rebased image will be tagged with :rebased (instead of
stripping the digest and pushing to :latest)

`crane rebase` now prints the full pushed image reference, instead of
just the digest (aiding embedding in other bash pipelines), and adds
annotations to aid future rebasings.

This also adds a bash test that covers the rebase case for detected base
image information.

…test.sh