wishlist: --yaml-stream should accept similar object structure to --multi

For composability, I like my jsonnet files to all evaluate to objects, in a style similar to that required for output by `--multi`. I want to actually output a YAML stream however (for piping to k8s' `kubectl`), so this means I now have "stub" jsonnet files everywhere that effectively import a bunch of jsonnet files, smoosh the objects together (possibly overriding some small number of values), and then end with some variant of `[objects[k] for k in std.objectFields(objects)]`.

This all works great, except now that new file can't be imported again in the same fashion. It would be neat if `--yaml-stream` just did something like that last expression (ie: take the object values) when presented with a file that evaluated to an object.

If the answer is "all this output tweaking is getting out of hand, we'd prefer you just write your own wrapper tool that uses the library" then I understand, and I'm ok with that.