update_engine: Transition to backuptool domain

* This way we can make backuptool permissive
  while leaving update_engine rules as clean as possible

Change-Id: Ied17f31f7d0258319371f3badc891c7a6ecee901
diff --git a/Android.bp b/Android.bp
index b7b4cd4..9814f88 100644
--- a/Android.bp
+++ b/Android.bp
@@ -195,6 +195,7 @@
         "liblz4",
         "libziparchive",
         "libprocessgroup",
+        "libselinux",
     ],
 }