qemuDomainDiskChangeSupported: Forbid alias change
    
    Since we have user aliases it may happen that users want to
    change it using 'update-device'. Instead of ignoring it silently,
    error out loudly. Note that we don't limit the check just for
    "ua-" prefixes because users might try to change libvirt
    generated aliases too.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
    Reviewed-by: John Ferlan <jferlan@redhat.com>