xencommons: write domain 0's domid to xenstore

libvchan's init_xs_srv (server-side xenstore-related initialization)
expects to find the current domain's domid at this xenstore key. libxl
(and xend) write this for domains they create. Do the same for domain 0,
allowing the use of libvchan in dom0.

Signed-off-by: Matthew Daley <mattjd@gmail.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/hotplug/NetBSD/rc.d/xencommons

@@ -68,8 +68,9 @@ xen_startcmd()
 
 	printf "\n"
 
-	printf "Setting domain 0 name.\n"
+	printf "Setting domain 0 name and domid.\n"
 	${BINDIR}/xenstore-write "/local/domain/0/name" "Domain-0"
+	${BINDIR}/xenstore-write "/local/domain/0/domid" 0
 }
 
 xen_stop()