#6303 introduced new bugs as it sets use_own_value to all ansible connection variables.
see the following lines in ansible/group_vars/all/creds.yml and ansible/group_vars/vm_host/creds.yml

vm_host_user: use_own_value
vm_host_password: use_own_value
vm_host_become_password: use_own_value

and a related task in ansible/testbed_add_vm_topology.yml

  - set_fact: ansible_user="{{ vm_host_user }}"
    when: vm_host_user is defined

These variables should have been unset by default or at least compared to default in testbed_add_vm_topology.yml

Fixing this would make the KVM Testbed configuration very simple (docs/testbed/README.testbed.VsSetup.md) and less misleading. The configuration would just ask to set ansible_user for STR-ACS-VSERV-01 (and even this could even been done automatically when setting the public keys).