def install_agent(agent_key, agent_version=1):
    '''
    Function downloads Server Density installation agent, and installs sd-agent
    with agent_key. Optionally the agent_version would select the series to
    use (defaults on the v1 one).

    CLI Example:

    .. code-block:: bash

        salt '*' serverdensity_device.install_agent c2bbdd6689ff46282bdaa07555641498
        salt '*' serverdensity_device.install_agent c2bbdd6689ff46282bdaa07555641498 2
    '''
    work_dir = os.path.join(__opts__['cachedir'], 'tmp')
    if not os.path.isdir(work_dir):
        os.mkdir(work_dir)
    install_file = tempfile.NamedTemporaryFile(dir=work_dir,
                                                   suffix='.sh',
                                                   delete=False)
    install_filename = install_file.name
    install_file.close()

    account_field = 'account_url'
    url = 'https://www.serverdensity.com/downloads/agent-install.sh'
    if agent_version == 2:
        account_field = 'account_name'
        url = 'https://archive.serverdensity.com/agent-install.sh'

    account = get_sd_auth(account_field)

    __salt__['cmd.run'](
        cmd='curl -L {0} -o {1}'.format(url, install_filename),
        cwd=work_dir
    )
    __salt__['cmd.run'](cmd='chmod +x {0}'.format(install_filename), cwd=work_dir)

    return __salt__['cmd.run'](
        cmd='{filename} -a {account} -k {agent_key}'.format(
            filename=install_filename, account=account, agent_key=agent_key),
        cwd=work_dir
    )