Use /mnt/storage for bind mounting package sandboxes.

Create a new slave bind mount at /mnt/storage and use this for
creating package sandboxes. This will help prevent package
specific data directories from getting duplicated and also make
handling bind mounts for packages with sharedUserIds easier.

Bug: 111890351
Test: manual
Change-Id: I0f590cc99a379d93f6db85bf56e8d274e3ea7488
2 files changed