init/NetBSD: move xenbackendd to xend init script

init/NetBSD: move xenbackendd to xend init script

xenbackendd is not needed by the xl toolstack, so move it's launch to
the xend script.

We have to iterate until we are sure there are no xend processes left,
since doing a single pkill usually leaves xend processes running.

Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
Acked-by: Christoph Egger <Christoph.Egger@amd.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Tested-by: Christoph Egger <Christoph.Egger@amd.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>