Currently, we are using 'tray_open' in QMP and 'tray-open' in
HMP. However, the QMP documentation was mistakenly using the
HMP version.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>