Test that Picker selection is updated correctly

Summary:
A React pull request broke the Picker: https://github.com/facebook/react/pull/6572
This pull request adds a test so that we prevent breakages like this in the future.

`PickerAndroidExample` in the UIExplorer before the breakage (video): https://vid.me/h5Rg
`PickerAndroidExample` in the UIExplorer after the breakage (video): https://vid.me/atFc

**Test plan**

`./scripts/run-android-local-integration-test.sh`

The test is failing, we can only merge this once React is fixed.

<img width="837" alt="screen shot 2016-05-04 at 5 13 31 pm" src="https://cloud.githubusercontent.com/assets/346214/15020827/aca8d718-121b-11e6-91f6-a338293d7d92.png">
Closes https://github.com/facebook/react-native/pull/7390

Differential Revision: D3305223

Pulled By: mkonicek

fbshipit-source-id: 89137812940c578efff3e76864ab7cadccc9f2ea

ReactAndroid/src/androidTest/js/PickerAndroidTestModule.js

@@ -52,6 +52,14 @@ var PickerAndroidTestApp = React.createClass({
           <Item label="item1" />
           <Item label="item2" />
         </Picker>
+        <Picker
+          mode="dropdown"
+          selectedValue={this.state.selected}
+          onValueChange={this.onValueChange}>
+          <Item label="item in sync 1" value={0} />
+          <Item label="item in sync 2" value={1} />
+          <Item label="item in sync 3" value={2} />
+        </Picker>
       </View>
     );
   },