Fix new user creation regression due to vold remount calls

When creating a new user, there's no need to call into vold when
setting up default system permissions for storage. This was otherwise
adding 2 seconds to the user creation time, causing a frozen screen
before showing "Switching to user ...".

Fix is to call the permission setup code synchronously and not
call into vold if the user hasn't been initialized yet.

Bug: 22356546
Change-Id: I4c8632813e8c0f2ac90da386691af439521bb25a