Add runtime property permissions for experiments

Bug: 120794191
Bug: 123524494
Test: set a property and ensure it can be read in AndroidRuntime.cpp

Change-Id: Ib37102f35e9987d3d9baff83c45571a5d632ad50
diff --git a/private/property_contexts b/private/property_contexts
index 3296a04..303832d 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -172,6 +172,7 @@
 persist.device_config.attempted_boot_count        u:object_r:device_config_boot_count_prop:s0
 persist.device_config.input_native_boot. u:object_r:device_config_input_native_boot_prop:s0
 persist.device_config.netd_native.           u:object_r:device_config_netd_native_prop:s0
+persist.device_config.runtime.           u:object_r:device_config_runtime_prop:s0
 
 apexd.                  u:object_r:apexd_prop:s0
 persist.apexd.          u:object_r:apexd_prop:s0