Allow apps to check attrs of /cache

Address the following denial:
type=1400 audit(0.0:261): avc: denied { getattr } for path="/cache" dev="mmcblk0p27" ino=2 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:cache_file:s0 tclass=dir permissive=0

Bug: 26823157
Change-Id: I937046969e92d96f2d31feceddd9ebe7c59bd3e6

app.te

@@ -237,6 +237,8 @@ allow appdomain adbd:unix_stream_socket connectto;
 allow appdomain adbd:fd use;
 allow appdomain adbd:unix_stream_socket { getattr getopt ioctl read write shutdown };
 
+allow appdomain cache_file:dir getattr;
+
 ###
 ### Neverallow rules
 ###