`cfssl sign` command does not expose the certificate's CA bundle

When using the `cfssl sign` CLI command to get a certificate signed by a remote cfssl server, it's useful to be able to get the CA bundle as well. The `cfssl sign` command, however, does not expose the API's "bundle = true" option; and calling the API directly does not work right now either due to #769.

Is there a different intended workflow for retrieving the bundle associated with a newly signed certificate? @lziest's comment on #769 suggests that this is an uncommon flow but I couldn't find another way to get a new certificate and its bundle in the same request.