for ansible issue concerning stacked SSH host key prompts

gistfile1.txt

given this inventory.yaml file: 
```
  ---
  all:
    children:
      bastion:
        hosts:
          test-bastion-0: 
      swarm_cluster:
        children:
          managers:
            hosts:
              test-0: 
          workers:
            hosts:
              test-1: 
```

this playbook: 
```
  ---
  - name: configure docker nodes 
    hosts: test_cluster
    gather_facts: yes
    remote_user: "{{ test_user.name }}"
    become_method: sudo
    become: True 
    # serial: 1
    vars: 
      ansible_become_pass: "{{ test_user.password }}"
      ansible_ssh_private_key_file: "{{ test_privatekey }}"
    roles:  
      - docker
``` 

this role: 
``` 
  ---
  - name: stop netfilter service  
    service: 
      name: netfilter-persistent 
      state: stopped

  - name: disable tcp forwarding & disable root login (sshd rules)
    template: 
      src: sshd_no_tcp_forwarding_config.jinja2
      dest: /etc/ssh/sshd_config
      owner: root 
      group: root 
      mode: 0600
      validate: "/usr/sbin/sshd -f %s -t"
      backup: yes
```

and this ansible.cfg file:
```
  [defaults]
  vault_password_file = ~/.vault_pass.txt
  roles_path    = ./roles
```