Credstore: Add rules to allow credstore read keystore2_enable property.

This is temporary, until keystore2 lands.

Test: CtsVerifier.
Change-Id: I8335e0eb48da682e66fceff9e31696d61235424b
diff --git a/private/property.te b/private/property.te
index e435628..a9c0c62 100644
--- a/private/property.te
+++ b/private/property.te
@@ -548,6 +548,7 @@
   -system_app
   -system_server
   -zygote
+  -credstore
 } keystore2_enable_prop:file no_rw_file_perms;
 
 neverallow {