Comment 4 for bug 1561947

Pretty sure it's https://github.com/openstack/glance_store/commit/1b782cee8552ec02f7303ee6f9ba9d1f2c180d07 -- we tried upgrading to different tags to isolate the error and noticed that 0.11.0 worked whilst 0.12.0 didn't. From there we walked through commits that touched the swift backend between these two tags and 142cf34c2f63900ac17f7e4c67a0f735deba84e4 worked fine but 1b782cee8552ec02f7303ee6f9ba9d1f2c180d07 caused an error to be raised when attempting to upload an image.