Remove multipart/form-data file upload

The requests 'files' parameter adds this 'Content-Type: multipart/form-data'
HTTP header and the whole multipart body data get stored with the object.
This also create a memory hog issue because files are loaded in memory before
being actually sent. This patch removes this behavior and restores what was
done before, ie: direct uploading.

This patches also fixes an issue in requests, when used with glance
CooperativeReader it mis-calculates content-length leading to chunked encoding
for raw upload.

Change-Id: Ie5b0a1078bedd33f09c6157f48b5f88116c589fa
Closes-Bug: #1280072
Closes-Bug: #1280275