fix "Unable to add user's profile photo id."

Commit a833763b enabled per-user
isolation, which requires that any files / processes which cross
user boundaries be marked with the mlstrustedsubject attribute.

system_app_data_file, used for storing a user's profile photos,
is not marked as such. As a result, users are unable to add profile
photos.

Addresses the following denial:

  avc: denied { write } for path="/data/data/com.android.settings/cache/TakeEditUserPhoto2.jpg" dev="mmcblk0p28" ino=82184 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:system_app_data_file:s0 tclass=file

Steps to reproduce:

  1.Flash & Factory the Deb device with tip-of-tree build
  2.Go to 'Settings-Users'
  3.Under users&profiles,click on Owner to add profile photo.
  4.Select 'Choose photo from Gallery' and select a photo.
  5.Then click the 'Done' button.
  6.Device showed the message as 'Unable to save the photo edits'.

OBSERVED RESULTS:
  Unable to add user's profile photo id. This issue is coming for all
  users(Restricted user,second user)also.

EXPECTED RESULTS:
  Device should allow to add profile photo id.

Bug: 19170844
Change-Id: If657dc09dd391e63ca85320f9cc1728580e51a15