Summary:
Based on https://github.com/facebook/react-native/pull/7470, fixing the case when an existing Android app uses React Native as well as 3rd-party React Native modules.
With this PR Gradle should always pick up React Native binaries from node_modules rather than fetching old binaries from JCenter.
Closes https://github.com/facebook/react-native/pull/7759
Differential Revision: D3348640
fbshipit-source-id: 7509eb54bba6e59cf7f4a116bf444fc4983d2d33