add recovery system interface to API

Adds android.os.RecoverySystem (marked as pending) to replace the
(hidden) com.android.internal.os.RecoverySystem.  RecoverySystem
contains methods for:

  - verifying the signature of an update package
  - rebooting to install a package
  - rebooting to wipe user data

(The reboot functions require "android.permission.REBOOT" and
"android.permission.ACCESS_CACHE_FILESYSTEM".)  Providing these
simplifies implementation of OTA update for device builders.

Change-Id: I63ce743b156e7a1a0327fd395b0e4a82c0eda79a
diff --git a/services/java/com/android/server/BootReceiver.java b/services/java/com/android/server/BootReceiver.java
index 84f0068..4279e00 100644
--- a/services/java/com/android/server/BootReceiver.java
+++ b/services/java/com/android/server/BootReceiver.java
@@ -23,12 +23,11 @@
 import android.os.Build;
 import android.os.DropBoxManager;
 import android.os.FileUtils;
+import android.os.RecoverySystem;
 import android.os.SystemProperties;
 import android.provider.Settings;
 import android.util.Log;
 
-import com.android.internal.os.RecoverySystem;
-
 import java.io.File;
 import java.io.IOException;