sepolicy[6/8]: allow vold to create files on external sdcard

This is required for ASEC support. Vold can already create and
access directories, but do not yet have the permission for files.

Signed-off-by: Humberto Borba <humberos@gmail.com>
Change-Id: I5082bbff692e5dc53c7000e4b3a293e42d33f901
Merge "sepolicy[6/8]: allow vold to create files on external sdcard" into android-4.4