ansible/ansible — pull request #952 by dagwieers (2012-08-28 13:28:21+00:00)
Title: Disable PasswordAuthentication when using -c ssh

If PasswordAuthentication is enabled (which is the default) ansible
will spawn (multiple) ssh's with a password-prompt which corrupts
the terminal, and cannot be properly used.

So it is better to not allow for password-based authentication using
-c ssh. The result is that authentication fails but Ansible
continues to work