update policy driver

Change-Id: I2450806d27455ae8304446f5b6054e14a66658b1
diff --git a/files/keystone.conf b/files/keystone.conf
index 64f0a66..5e5bfeb 100644
--- a/files/keystone.conf
+++ b/files/keystone.conf
@@ -35,7 +35,7 @@
 driver = keystone.token.backends.kvs.Token
 
 [policy]
-driver = keystone.policy.backends.simple.SimpleMatch
+driver = keystone.policy.backends.rules.Policy
 
 [ec2]
 driver = keystone.contrib.ec2.backends.sql.Ec2