Unlock all users before moving or migrating.

When moving apps or shared storage between storage media on FBE
devices, we need all users to be unlocked to successfully move
the data.  This change asks the user to enter the credentials for
any locked users as part of the moving/migration wizard flows.

To do this we relax Utils.enforceSameOwner() to let us prompt for the
credentials of unrelated users, but we carefully only extend this
capability to callers interacting with the "internal" activities,
which require the MANAGE_USERS permission.

Test: builds, boots, users are unlocked before moving
Bug: 29923055, 25861755
Change-Id: Ifaeb2557c4f8c4354e1d380eaa0e413768ee239f