def create_tag_and_push(version):
    "Create a git tag for `version` and push it to origin."
    assert version not in tags()
    git('config', 'user.name', 'Travis CI on behalf of Austin Bingham')
    git('config', 'user.email', 'austin@sixty-north.com')
    git('config', 'core.sshCommand', 'ssh -i deploy_key')
    git(
        'remote', 'add', 'ssh-origin',
        'git@github.com:sixty-north/cosmic-ray.git'
    )
    git('tag', version)

    subprocess.check_call([
        'ssh-agent', 'sh', '-c',
        'chmod 0600 deploy_key && ' +
        'ssh-add deploy_key && ' +
        # 'git push ssh-origin HEAD:master &&'
        'git push ssh-origin --tags'
    ])
Create a git tag for `version` and push it to origin.