Return a list of users on a MySQL server

    CLI Example:

    .. code-block:: bash

        salt '*' mysql.user_list

def user_list(**connection_args):
    '''
    Return a list of users on a MySQL server

    CLI Example:

    .. code-block:: bash

        salt '*' mysql.user_list
    '''
    dbc = _connect(**connection_args)
    if dbc is None:
        return []
    cur = dbc.cursor(MySQLdb.cursors.DictCursor)
    try:
        qry = 'SELECT User,Host FROM mysql.user'
        _execute(cur, qry)
    except MySQLdb.OperationalError as exc:
        err = 'MySQL Error {0}: {1}'.format(*exc.args)
        __context__['mysql.error'] = err
        log.error(err)
        return []
    results = cur.fetchall()
    log.debug(results)
    return results