Summary: @​public

We need to start using the `private-cli` for the new asset system. Note this is a breaking change! People will have to upgrade their workflows/scripts to start using the new cli. Otherwise we'd need to build a thin adapter that is aware of both APIs which is something we;d like to avoid. The major API changes are:
  - API is now `entry-file` based instead of `url` based.
  - /s/--out/--bundle-output
  - /s/--out/--sourcemap-output

Also these parameters have no longer default values, you need to specify them. For instance, if you want to generate the sourcemaps you need to pass in the `--sourcemap-output` option

Lastly, additional project roots or asset roots need to be specified on the `rn-cli.config.js`.

Reviewed By: @frantic

Differential Revision: D2533877

fb-gh-sync-id: a45f9095fdf9442a9106ea7bb6a6b7f651d25273