role_install -p playbook.yml
role_install -e ssh://github.com/github_owner/github_repo.git 

# playbook.yml defines
vars:
  install_roles:
    - {uri: 'ssh://github.com/github_owner/github_repo.git'}
    - {uri: 'ssh://github.com/github_owner/github_repo.git', name: 'repo'}