can not support user-defined usage of chunked body

Description
===========
Chunked body dramatically slows down of uploading
images to glance under volume-backed image context
or leads to failure as some volume backend can not
extend in-use volume such as active-active volume
of AS5600. It's better to support user-defined usage
of chunked body so that users can determine whether
corresponding volume is extended than to force users
to utilize chunked body.

Steps to reproduce
==================
1. Upload a image to glance under volume-backed image
context. You can configure the volume-backed image as
follows: https://docs.openstack.org/cinder/queens/admin/blockstorage-volume-backed-image.html
2. Inspect the corresponding volume's status.

Expected result
===============
Users can determine whether corresponding volume is extended.

Actual result
=============
Corresponding volume is always alextended so that the upload
process will be considerably slower than normal.

Environment
===========
master branch of OpenStack

Logs & Configs
==============
None

Implicated codes
==============
https://opendev.org/openstack/python-glanceclient/src/branch/master/glanceclient/common/http.py#L110