CA-204484: Move cancellation logic to slave
CA-204484: Move cancellation logic to slave

If a cancel causes the VM to be shutdown, a hard_reboot won't be
able to find the host to forward it to. If we forward first, we
can be sure the reboot will be able to start the guest.

Signed-off-by: Jon Ludlam <e7e3380887a8f95cc9dc4f0d51dedc7e849a287a@citrix.com>

jjd27/xen-api,jjd27/xen-api,jjd27/xen-api,jjd27/xen-api,jjd27/xen-api,jjd27/xen-api