Allow vold to create files at /mnt/user/.*

Bug: 121099965
Test: manual
Change-Id: I940868eb984399763d7346a201e37cb07fb12333

public/vold.te

@@ -78,6 +78,7 @@ allow vold { mnt_media_rw_stub_file storage_stub_file }:dir { mounton create rmd
 # Manage per-user primary symlinks
 allow vold mnt_user_file:dir { create_dir_perms mounton };
 allow vold mnt_user_file:lnk_file create_file_perms;
+allow vold mnt_user_file:file create_file_perms;
 
 # Allow to create and mount expanded storage
 allow vold mnt_expand_file:dir { create_dir_perms mounton };