List all available locations

def avail_locations(call=None):
    '''
    List all available locations
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_locations function must be called with '
            '-f or --function, or with the --list-locations option'
        )

    ret = {}

    params = {'Action': 'DescribeRegions'}
    result = aws.query(params,
                       location=get_location(),
                       provider=get_provider(),
                       opts=__opts__,
                       sigver='4')

    for region in result:
        ret[region['regionName']] = {
            'name': region['regionName'],
            'endpoint': region['regionEndpoint'],
        }

    return ret