Remove Location header from createImage and createBackup responses

This is explained in detail in bug 1679285, but the createImage API returns a Location header in the response which is built from the CONF.glance.api_servers configuration within Nova that is most likely using internal addresses for Glance, making it unusable for the end user.

Client code like Tempest and python-novaclient have always ignored the Location header in the response and just parsed the URL to get the image ID and use it for their own GET /v2/images/{image_id} request.

Also, the URL in the Location header response is unversioned, but reading the image service API reference docs for the versions document and the examples, there is always a versioned prefix on the URL, e.g. GET /v1/images or GET /v2/images. The fact the URL returned from nova is unversioned likely means this is a legacy artifact before Glance was split out from Nova.

This blueprint proposes to remove the Location header in the response and just return the image_id in a response body dict with a new microversion for the createImage API.

We have the same issue in the createBackup server action API too.