Add direct upload feature for file glance backend

This blueprint aims to support for the direct upload feature
for "glance image file backend" when taking vm snapshot.

Problem description
===================

Supporting for direct downloads of glance locations is already added
by plug-in modules.[1]
And this feature only can support downloading not uploading.

In current version of nova if you take snapshot of a running server,
nova will upload the image to glance server.
if it creates multiple snapshot at the same time,
glance server will receive heavy load and traffic.

it would be better to upload directly to the backend store
instead of sending all of the image size through glance server.

Added new file upload scheme for Nova.
With that change Nova can upload snapshot images directly
from snapshot working directory to glance file backend

Proposed change
===============

Instead of sending through glance node,
nova-compute service can directly upload image
from snapshot working directory to glance file backend.

the workflow is simple as follows:

    1. Create an image from vm snapshot.(nova image-create)
    2. copy that image to glance file backend.
    3. if anything failes in the process,
        the image will be uploaded through glance node as before.