Make v1 pull/push output consistent with v2

- Use layer DiffIDs for progress output in v1 push. This makes the
  output consistent with v2 pushes, which means that a fallback to v1
  won't start progress bars for a different set of IDs.

- Change wording used in v1 status updates to be consistent with v2.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>