Add persist.vendor.overlay. to properties

Allow the system_server to change. Allow the zygote to read it as well.

Test: Have system_server set a property
Change-Id: Ie90eec8b733fa7193861026a3a6e0fb0ba5d5318
diff --git a/private/property_contexts b/private/property_contexts
index df82223..51b9ff8 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -56,6 +56,8 @@
 persist.service.        u:object_r:system_prop:s0
 persist.service.bdroid. u:object_r:bluetooth_prop:s0
 persist.security.       u:object_r:system_prop:s0
+persist.vendor.overlay.  u:object_r:overlay_prop:s0
+ro.boot.vendor.overlay.  u:object_r:overlay_prop:s0
 
 # Boolean property set by system server upon boot indicating
 # if device owner is provisioned.