Use MaaS node key when on_maas

Change-Id: Ie5708aac996647ee532d33a82ec5e9af468645a8
(cherry picked from commit 057a8833bb8f5627ed2c05a307ae4149f3131020)
diff --git a/vars/cord_defaults.yml b/vars/cord_defaults.yml
index 541569f..12ce207 100644
--- a/vars/cord_defaults.yml
+++ b/vars/cord_defaults.yml
@@ -4,6 +4,8 @@
 # turn this off, or override when running playbook with --extra-vars="on_maas=False"
 on_maas: True
 
+maas_node_key: /etc/maas/ansible/id_rsa
+
 openstack_version: kilo
 
 juju_config_name: cord