Allow update_engine to read postinstall_mnt_dir

am: 8f687053

Change-Id: Ib0ba78601046e6574cbb44752ebc431791a62df6

public/update_engine_common.te

@@ -19,7 +19,7 @@ allow update_engine_common rootfs:file r_file_perms;
 
 # Allow update_engine_common to mount on the /postinstall directory and reset the
 # labels on the mounted filesystem to postinstall_file.
-allow update_engine_common postinstall_mnt_dir:dir mounton;
+allow update_engine_common postinstall_mnt_dir:dir { mounton getattr search };
 allow update_engine_common postinstall_file:filesystem { mount unmount relabelfrom relabelto };
 allow update_engine_common labeledfs:filesystem relabelfrom;