Change user 0 directory back for compatibility

The PackageManagerTests aren't designed for multiple users yet, so they
fail. Since multiple users aren't supported yet, just change the default
data directory for user 0 back to how it was previously. This fixes the
existing tests and doesn't get anyone's hopes up since they won't see
/data/user/0/pacakge when we don't support multiple users yet.

Bug: 4380006
Change-Id: Iedcc3115b000759c0013ba6878e13cd2358897da