I know that the OpenStack delivery plugin is only at "technology preview" status, but I decided to try and use it anyway and provide feedback from my experience with it.
1) I encountered a 404 error. This turned out to be invalid urls in openstack-plugin.rb. I had to remove all instances of "/v1" from the urls.
2) When overwrite is selected, it looks like the code expects a filtered list of images that match the image name you are trying to upload. The list that is returned by get_images is *not* filtered. So, what happened was that it returned *ALL* images and proceeded to delete them. (Good thing the system I was testing this out on was in a development state and that I know the admins )
However, once #1 was fixed, and disregarding #2, the post_image worked perfectly. I was able to upload and register my image.
The OpenStack install was from the "Cactus" release. I checked the docs for "Diablo" and the API is the same for that release.