Summary:Added a `root` option to the `run-android` command allowing to run it from a parent directory.
Use case: project is organized like this
```
- api
- apps
---- web
---- react-native
- package.json
```
You can use the root option on `react-native start` but not on `run-android`. This pr fixes that.
Closes https://github.com/facebook/react-native/pull/5597
Differential Revision: D2959523
Pulled By: mkonicek
fb-gh-sync-id: 03fb74b201fe9e89bf6fab80c9a98ca708464261
shipit-source-id: 03fb74b201fe9e89bf6fab80c9a98ca708464261