Make the application persistent

* Should help with not having services killed
* System app only, but shouldn't cause any errors if it's a user-app

Change-Id: Iee2a662da074753008f6896cfa155acbeddcc974

Author: chirayudesai

play-services-core/src/main/AndroidManifest.xml

@@ -114,6 +114,7 @@
         android:fullBackupOnly="true"
         android:extractNativeLibs="false"
         android:forceQueryable="true"
+        android:persistent="true"
         android:icon="@mipmap/ic_core_service_app"
         android:label="@string/gms_app_name"
         android:theme="@style/Theme.AppCompat.DayNight">