Update AppRTCMobile tests to use JUnit4.

webrtc/examples/androidtests/AndroidManifest.xml

-<?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="org.appspot.apprtc.test"
-    android:versionCode="1"
-    android:versionName="1.0" >
+<!--
+ *  Copyright 2017 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+-->
+
+<manifest
+      xmlns:android="http://schemas.android.com/apk/res/android"
+      package="org.appspot.apprtc.test">
 
     <uses-sdk android:minSdkVersion="13" android:targetSdkVersion="21" />
 
-    <instrumentation
-        android:name="android.test.InstrumentationTestRunner"
-        android:targetPackage="org.appspot.apprtc" />
+    <uses-permission android:name="android.permission.RUN_INSTRUMENTATION" />
 
     <application>
         <uses-library android:name="android.test.runner" />
     </application>
 
-</manifest>
+    <instrumentation android:name="android.support.test.runner.AndroidJUnitRunner"
+        android:targetPackage="org.appspot.apprtc"
+        android:label="Tests for AppRTCMobile"/>
+</manifest>