Comments, docstrings and live test names cited item IDs of a roadmap
that is not part of the repository. They now say what is meant, or
nothing where the sentence stands without them. Test assertions and
behavior are unchanged.
Web form: the cache mode and the UEFI firmware value were checked only
after the disk volume had been created; an invalid one answered 500 and
left the volume. All checks now run before any allocation. Volumes the
request creates are removed on any failure up to the definition; ones
that cannot be removed are reported. After the definition the VM uses
them, so a later failure keeps them.
API: the new volume was never removed when the definition failed, and
the error was a 500. It is removed now and a libvirt error returns 400.
