emulator: bump revision of sdk system images to 4 am: fbaf0884db am: eb7ac42aa3
am: b312ed8ba0

* commit 'b312ed8ba0f3ebc2d7551b8eded88fcfa8065773':
  emulator: bump revision of sdk system images to 4

Change-Id: If6eb98f88db646271fda4da13ce3531a0e8f7b4e