Allow access to media_rw_data_file for now.

With sdcardfs, we no longer have a separate sdcardd acting as
an intermediate between the outside world and /data/media.
Unless we modify sdcardfs to change contexts, we need these.
Added for: adbd, kernel, mediaserver, and shell

Remove this patch if sdcardfs is updated to change the
secontext of fs accesses.

Bug: 27915475
Bug: 27937873

Change-Id: I25edcfc7fb8423b3184db84040bda790a1042724