Make default_prop only readable from coredomain

default_prop has been readable from coredomain and appdomain. It's too
broad, because default_prop is a context for properties which don't have
matching property_contexts entries.

From now on, only coredomain can read default_prop. It's still broad,
but at least random apps can't read default_prop anymore.

Bug: 170590987
Test: SELinux denial boot test for internal devices
Change-Id: Ieed7e60d7e4448705c70e4f1725b2290e4fbcb4a
4 files changed