get list of available packages

    CLI Example:

    .. code-block:: bash

        salt-cloud --list-sizes

def avail_sizes(call=None):
    '''
    get list of available packages

    CLI Example:

    .. code-block:: bash

        salt-cloud --list-sizes
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_sizes function must be called with '
            '-f or --function, or with the --list-sizes option'
        )

    rcode, items = query(command='my/packages')
    if rcode not in VALID_RESPONSE_CODES:
        return {}
    return key_list(items=items)