Make provision to bypass chunked transfer encoding

As python-glanceclients uploads image data with "Transer-Encoding: chunked", the requests library does not support transferring the header "Content-Length" with the request. This works fine in most cases but can become an issue if Glance is using Cinder as the backend. An HTTP chunked transfer inherently has no known data size and because of this Glance will perform an iterative "resize-before-write" process to gradually grow the Cinder volume 1 GB at a time until it receives the last of the image data. The problem
with this is that the Cinder volume must be detached and then re-attached each iteration. This process can be very slow.

This is also the case when glance is using ceph (RBD) as a backend where it does this "resize-before-write" operation as well which can be time consuming.

If you configure glance to use s3 as a backend then you will not be able to use multipart-upload feature of s3 backend as you don't know the image size3 in advance.