Allow querying isPreCreated to anyone with INTERACT_ACROSS_USERS permission.

This:
1. Makes this call more consistent with most of the other accessors.
2. Allows shell to access it, which is needed for commands like
"am stop-user -w". Shell does not have MANAGE_USERS, but it has
INTERACT_ACROSS_USERS.

Another way to fix 2 would be to clear binder identity in UC.stopSingleUserLU,
but that seemed like a more risky change.

Fixes: 150929990
Test: "am stop-user -w" does not throw security exception
Change-Id: I6caa43cd8cd7083f0b9dbc515c53dee181030761