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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def join_cluster(host, user='rabbit', ram_node=None, runas=None):
    '''
    Join a rabbit cluster

    CLI Example:

    .. code-block:: bash

        salt '*' rabbitmq.join_cluster rabbit.example.com rabbit
    '''
    cmd = [RABBITMQCTL, 'join_cluster']
    if ram_node:
        cmd.append('--ram')
    cmd.append('{0}@{1}'.format(user, host))

    if runas is None and not salt.utils.platform.is_windows():
        runas = salt.utils.user.get_user()
    stop_app(runas)
    res = __salt__['cmd.run_all'](cmd, reset_system_locale=False, runas=runas, python_shell=False)
    start_app(runas)

    return _format_response(res, 'Join')