Add back projectRoots option to packager CLI command

Summary: Adding this to the CLI again (like: 8e7cfcd053 (diff-75e3fc051b7c5100b4681e8a8f62615bL45))

Fix #2390
Closes https://github.com/facebook/react-native/pull/4065

Reviewed By: svcscm

Differential Revision: D2652032

Pulled By: mkonicek

fb-gh-sync-id: 7162983c24f6e08ecc8f7f410e9b756471d88631

local-cli/server/server.js

@@ -35,6 +35,10 @@ function _server(argv, config, resolve, reject) {
     type: 'string',
     description: 'add another root(s) to be used by the packager in this project',
   }, {
+    command: 'projectRoots',
+    type: 'string',
+    description: 'override the root(s) to be used by the packager',
+  },{
     command: 'assetRoots',
     type: 'string',
     description: 'specify the root directories of app assets'