ssh config を汚さずに Ansible で Vagrant ホストを扱う ref: http://qiita.com/janus_wel/items/faac04f2ec2cdb50d074

ansible.cfg

[defaults]
hostfile = .vagrant/provisioners/ansible/inventory/vagrant_ansible_inventory
remote_user = vagrant
private_key_file = ~/.vagrant.d/insecure_private_key
host_key_checking = False

generate-inventory.yml

--- # generate ansible inventory file with Vagrant
- hosts: default
  tasks:
    - name: ping
      action: ping

Vagrantfile

  config.vm.provision "ansible" do |ansible|
    ansible.host_key_checking = false
    ansible.playbook = "generate-inventory.yml"
  end