Return a dict of all available VM images on the cloud provider.

def avail_images(call=None):
    '''
    Return a dict of all available VM images on the cloud provider.
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_images function must be called with '
            '-f or --function, or with the --list-images option'
        )

    ret = {}
    conn = get_conn(service='SoftLayer_Product_Package')
    for category in conn.getCategories(id=50):
        if category['categoryCode'] != 'os':
            continue
        for group in category['groups']:
            for price in group['prices']:
                ret[price['id']] = price['item'].copy()
                del ret[price['id']]['id']
    return ret