The nova API we're using to delete a server volume attachment needs to
be handed a volume, not a volume attachment.
Also make sure that we create an error if the volume isn't actually
attached to the server.
Signed-off-by: Dr. Jens Harbott <harbott@osism.tech>
Co-authored-by: Stephen Finucane <sfinucan@redhat.com>
Change-Id: I12abd3787ea47acb4da282d00fdc1989405a0564