Added private key file to ssh bastion conf (#1563)

* Added private key file to ssh bastion conf

* Used regular if condition insted of inline conditional

roles/bastion-ssh-config/templates/ssh-bastion.conf

@@ -16,6 +16,6 @@ Host {{ bastion_ip }}
   ControlPersist 5m
 
 Host {{ vars['hosts'] }}
-  ProxyCommand ssh -W %h:%p {{ real_user }}@{{ bastion_ip }}
+  ProxyCommand ssh -W %h:%p {{ real_user }}@{{ bastion_ip }} {% if ansible_ssh_private_key_file is defined %}-i {{ ansible_ssh_private_key_file }}{% endif %}
   StrictHostKeyChecking no
 {% endif %}