Checks if user with given alias exists.

    .. versionadded:: 2016.3.0

    :param alias: user alias
    :param _connection_user: Optional - zabbix user (can also be set in opts or pillar, see module's docstring)
    :param _connection_password: Optional - zabbix password (can also be set in opts or pillar, see module's docstring)
    :param _connection_url: Optional - url of zabbix frontend (can also be set in opts, pillar, see module's docstring)

    :return: True if user exists, else False.

    CLI Example:
    .. code-block:: bash

        salt '*' zabbix.user_exists james

def user_exists(alias, **kwargs):
    '''
    Checks if user with given alias exists.

    .. versionadded:: 2016.3.0

    :param alias: user alias
    :param _connection_user: Optional - zabbix user (can also be set in opts or pillar, see module's docstring)
    :param _connection_password: Optional - zabbix password (can also be set in opts or pillar, see module's docstring)
    :param _connection_url: Optional - url of zabbix frontend (can also be set in opts, pillar, see module's docstring)

    :return: True if user exists, else False.

    CLI Example:
    .. code-block:: bash

        salt '*' zabbix.user_exists james
    '''
    conn_args = _login(**kwargs)
    ret = {}
    try:
        if conn_args:
            method = 'user.get'
            params = {"output": "extend", "filter": {"alias": alias}}
            ret = _query(method, params, conn_args['url'], conn_args['auth'])
            return True if ret['result'] else False
        else:
            raise KeyError
    except KeyError:
        return ret