Settings: use DefaultContainerService for all file operations

For devices with non-emulated storage, the system uid is not allowed
to access the storage (to prevent system_server from being killed
on UMS mount). Old code remain that make file access directly, change
those to use DefaultContainerService

Depends on http://review.cyanogenmod.org/28179

Change-Id: Ie6bdaf27249daeabdc7f0ef1d73d484764ee35f0