dex2oat fails when upgrading unlabeled asec containers.

Steps to reproduce:

1) Install a forward locked app on Android 4.1
  adb install -l foo.apk
2) Upgrade to tip-of-tree

Addresses the following denial:

  <4>[  379.886665] type=1400 audit(1405549869.210:4): avc: denied { read } for pid=2389 comm="dex2oat" path="/mnt/asec/jackpal.androidterm-1/pkg.apk" dev=dm-0 ino=12 scontext=u:r:dex2oat:s0 tcontext=u:object_r:unlabeled:s0 tclass=file

(cherry picked from commit 270be6e8)

Change-Id: I58dc6ebe61a5b5840434077a55f1afbeed602137