Update vold to prepare package sandboxes for primary volume.

Vold is updated to create package specific sandboxes for primary
volume and mount them at
"/mnt/user/<user-id>/package/<package-name>/<primary-label>".
This will later be mounted at /storage when a new process starts.

Bug: 111890351
Test: Manually verified that a package has access to "/sdcard" and
      "/storage/emulated/0", both of which are just the package specific
      sandboxes and the package doesn't have access to other sandboxes
      and can't see other package names.

Change-Id: I72dc8ae9eb2260a298159c5de18387dad2f9de48
6 files changed