Add more sane multi-profile app attribution.

Due to issues w.r.t. attribution across multiple users, we originally
duplicated the previous implementation which zeroed out the sizes. This,
however, caused system bloat due to the change in how we calculate the
system size.

By attributing apps which do not exist in the primary profile to the
first user that shows up with it installed, we can avoid accidentally
attributing it to the system size.

Bug: 62623731
Test: Settings unittest & Settings robotest
Change-Id: I9514c9ecef62ea6270723f62e6bf27c69b75f180