Use MaaS node key when on_maas

Change-Id: Ie5708aac996647ee532d33a82ec5e9af468645a8
(cherry picked from commit 057a8833bb8f5627ed2c05a307ae4149f3131020)
diff --git a/roles/xos-vm-install/templates/xos-setup-vars.yml.j2 b/roles/xos-vm-install/templates/xos-setup-vars.yml.j2
index 9a0afbb..cb96393 100644
--- a/roles/xos-vm-install/templates/xos-setup-vars.yml.j2
+++ b/roles/xos-vm-install/templates/xos-setup-vars.yml.j2
@@ -14,3 +14,9 @@
 service_profile_repo_url: "{{ service_profile_repo_url }}"
 service_profile_repo_dest: "{{ service_profile_repo_dest }}"
 service_profile_repo_branch: "{{ service_profile_repo_branch }}"
+
+{% if on_maas %}
+node_private_key: "{{ maas_node_key }}"
+{% else %}
+node_private_key: "~/.ssh/id_rsa"
+{% endif %}