Allow vendor_init to relabelfrom unlabeled.

This will be needed if vendors remove a label, as vendor_init would
need to relabel from it (which would be unlabeled) to the new label.

Test: Build policy.
Change-Id: Ieea0fcd7379da26b2864b971f7773ed61f413bb9

public/vendor_init.te

@@ -55,6 +55,8 @@ allow vendor_init {
   -vold_metadata_file
 }:dir { create search getattr open read setattr ioctl write add_name remove_name rmdir relabelfrom };
 
+allow vendor_init unlabeled:{ dir notdevfile_class_set } { getattr relabelfrom };
+
 allow vendor_init {
   file_type
   -core_data_file_type