Add boot mode where only "core apps" are started.

A core app is one that has coreApp="true" in its manifest tag.

The system can successfully boot (though a little painfully) with
only framework-res.apk, SettingsProvider.apk, SystemUI.apk,
DefaultContainerService.apk, and Launcher2.apk set as core apps.

Currently this boot mode is always turned off.

Change-Id: Ieaa4a8031c2c391a12996aa8d8b1d65fc2b09d6b
diff --git a/packages/DefaultContainerService/AndroidManifest.xml b/packages/DefaultContainerService/AndroidManifest.xml
index 0f47482..319eb8d 100755
--- a/packages/DefaultContainerService/AndroidManifest.xml
+++ b/packages/DefaultContainerService/AndroidManifest.xml
@@ -1,5 +1,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-        package="com.android.defcontainer">
+        package="com.android.defcontainer" coreApp="true">
     <uses-permission android:name="android.permission.ACCESS_DOWNLOAD_MANAGER"/>
     <uses-permission android:name="android.permission.ACCESS_ALL_DOWNLOADS"/>
     <uses-permission android:name="android.permission.ASEC_ACCESS"/>