Disk and media mutation views (add_new_vol, add_existing_vol, edit_volume,
delete_vol, detach_vol, add_cdrom, detach_cdrom, mount_iso, unmount_iso)
were reachable by any owner with is_change, although the UI only shows the
Disk tab to superusers. An ordinary user could delete any volume on the
compute or attach arbitrary host files to their VM.
- Require superuser for all disk/media views, matching the UI.
- delete_vol resolves the volume from the VM's own disk XML by dev and
ignores the posted storage/name.
- Validate bus/cache/io/discard/detect_zeroes against the hypervisor's
lists, and format/serial/volume name against strict patterns.
- add_existing_vol only accepts volumes that exist in the selected pool.
- edit_volume only accepts a dev attached to the VM.
- vrtManager: escape all values interpolated into disk XML and pass dev
as an XPath variable in detach_disk/edit_disk.
