Pass private key file from parent Ansible to Kubespray

The private key file is not part of the inventory in our case, but
it's a global Ansible parameter. Make sure that we carry the same
--private-key parameter from parent Ansible run into Kubespray.

Change-Id: If6e341ee52f9d4944ee1855d3339e26b9a485dd0

extraconfig/services/kubernetes-master.yaml

@@ -154,6 +154,7 @@ outputs:
                   -i '{{playbook_dir}}/kubespray/inventory.yml'
                   --skip-tags docker,bastion-ssh-config
                   --extra-vars '@{{playbook_dir}}/kubespray/global_vars.yml'
+                  --private-key '{{ansible_ssh_private_key_file}}'
                   '{{playbook_dir}}/kubespray/playbook.yml'
                   {%- endif -%}
             - name: print kubespray command