Restrict access to Bluetooth system properties

This removes access to Bluetooth system properties from arbitrary
SELinux domains. Access remains granted to init, bluetooth, and
system_app domains. neverallow rules / CTS enforce that access is not
granted to Zygote and processes spawned from Zygote expcept for
system_app and bluetooth.

The reason is that some of these properties may leak persistent
identifiers not resettable by the user.

Test: Bluetooth pairing and data transfer works
Bug: 33700679
Change-Id: Icdcb3927a423c4011a62942340a498cc1b302472
diff --git a/private/property_contexts b/private/property_contexts
index 39e8a8d..80476cc 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -61,7 +61,9 @@
 ro.boot.vendor.overlay.  u:object_r:overlay_prop:s0
 ro.boottime.             u:object_r:boottime_prop:s0
 ro.serialno             u:object_r:serialno_prop:s0
+ro.boot.btmacaddr       u:object_r:bluetooth_prop:s0
 ro.boot.serialno        u:object_r:serialno_prop:s0
+ro.bt.                  u:object_r:bluetooth_prop:s0
 
 # Boolean property set by system server upon boot indicating
 # if device owner is provisioned.