Ensure that /tftpboot/pxelinux.cfg is owned by Ironic

The pxelinux.cfg directory gets created but isn't owned by the correct
user. This patch ensures that the permissions are correctly updated.

Change-Id: Ifcb80018b72d40c5d4eccf059d1c3442b71be6f8

ansible/roles/ironic/templates/ironic-pxe.json.j2

@@ -21,5 +21,12 @@
             "owner": "root",
             "perm": "0644"
         }
+    ],
+    "permissions": [
+        {
+            "path": "/tftpboot/pxelinux.cfg",
+            "owner": "ironic:ironic",
+            "recurse": true
+        }
     ]
 }