Set policy_file in the oslo_policy group

policy_file in DEFAULT is deprecated

Change-Id: I6698a810d5e6c395a18aed8066e61f8c4bae2408
diff --git a/lib/ironic b/lib/ironic
index 4ac0100..4a37f0a 100644
--- a/lib/ironic
+++ b/lib/ironic
@@ -296,7 +296,7 @@
 # API specific configuration.
 function configure_ironic_api {
     iniset $IRONIC_CONF_FILE DEFAULT auth_strategy keystone
-    iniset $IRONIC_CONF_FILE DEFAULT policy_file $IRONIC_POLICY_JSON
+    iniset $IRONIC_CONF_FILE oslo_policy policy_file $IRONIC_POLICY_JSON
 
     # TODO(Yuki Nishiwaki): This is a temporary work-around until Ironic is fixed(bug#1422632).
     # These codes need to be changed to use the function of configure_auth_token_middleware