Android 4.2 migration fixes.

If /data/media/0 exists after a data wipe, place the .layout_version file
into /data to prevent Android 4.2 from running the data migration.
This fixes the bug where multiple migrations end up with the following dirs:
/sdcard/0/0/0/0. One /0 per each wipe.

Change-Id: I0adea3840c4ad6abcdead4c488ac5012b3744429