Return a list of the image sizes that are on the provider

def avail_sizes(call=None):
    '''
    Return a list of the image sizes that are on the provider
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_sizes function must be called with '
            '-f or --function, or with the --list-sizes option'
        )

    params = {'Action': 'DescribeInstanceTypes'}
    items = query(params=params)

    ret = {}
    for image in items['InstanceTypes']['InstanceType']:
        ret[image['InstanceTypeId']] = {}
        for item in image:
            ret[image['InstanceTypeId']][item] = six.text_type(image[item])

    return ret