Breaking change: Move bundle to private-cli

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

cli.js

@@ -1,4 +1,4 @@
- /**
+/**
  * Copyright (c) 2015-present, Facebook, Inc.
  * All rights reserved.
  *
@@ -8,4 +8,8 @@
  */
 'use strict';
 
+require('./packager/babelRegisterOnly')([
+  /private-cli\/src/
+]);
+
 module.exports = require('./local-cli/cli.js');