Fix: D8450498 breaks test_end_to_end job (#19910)

Summary:
Closes https://github.com/facebook/react-native/pull/19910

Because of the way react-native local-cli communicates with metro, getWatchFolders function was always returning an empty array that triggered an error.

Reviewed By: hramos

Differential Revision: D8650733

fbshipit-source-id: 502ca469cdbfa04dab5127c1e330dc1d34fc02f8

local-cli/util/Config.js

@@ -78,6 +78,7 @@ const Config = {
     ],
     getProjectRoots,
     getPolyfills,
+    getWatchFolders: () => [getProjectPath()],
     getResolverMainFields: () => ['react-native', 'browser', 'main'],
     getTransformModulePath: () =>
       require.resolve('metro/src/reactNativeTransformer'),