Add label for persist.pm.mock-upgrade

This property is used for testing purposes when verifying the
behavior when an OTA occurs. It should be readable by the
system server, and be settable by the shell.

Test: Set property from shell, read with PackageManager
Bug: 140992644
Change-Id: I39ad9b7961208f02fa45011215c2ff5ac03b7380
diff --git a/private/system_server.te b/private/system_server.te
index a7f9b13..34e832b 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -628,6 +628,9 @@
 # Read gsid.image_running.
 get_prop(system_server, gsid_prop)
 
+# Read the property that mocks an OTA
+get_prop(system_server, mock_ota_prop)
+
 # Create a socket for connections from debuggerd.
 allow system_server system_ndebug_socket:sock_file create_file_perms;