Pass testID down in Modal

Summary:
Changelog:
[General][Fixed] - Modal accepts a testID but didn't forward it to RCTModalHostView, therefore not making it show up for e2e tests depending on viewhierarchy.

Reviewed By: motiz88

Differential Revision: D32354377

fbshipit-source-id: 51df3a1f81c4b77240e83101b367b033ce98b0c7

Libraries/Modal/Modal.js

@@ -264,7 +264,8 @@ class Modal extends React.Component<Props> {
         // $FlowFixMe[method-unbinding] added when improving typing for this parameters
         onStartShouldSetResponder={this._shouldSetResponder}
         supportedOrientations={this.props.supportedOrientations}
-        onOrientationChange={this.props.onOrientationChange}>
+        onOrientationChange={this.props.onOrientationChange}
+        testID={this.props.testID}>
         <VirtualizedListContextResetter>
           <ScrollView.Context.Provider value={null}>
             <View