xenapi: add username to vncviewer command

Devstack prints out an instruction, how to look at the virtual machine's
console. The command did not include the username, so if the user had a
config file to use a different username for that network, the command
failed.

Change-Id: I5dd49169c45e26e8d2bb3d5920a1b7fa584be50f
diff --git a/tools/xen/install_os_domU.sh b/tools/xen/install_os_domU.sh
index 997644d..a012a08 100755
--- a/tools/xen/install_os_domU.sh
+++ b/tools/xen/install_os_domU.sh
@@ -181,7 +181,7 @@
     mgmt_ip=$(echo $XENAPI_CONNECTION_URL | tr -d -c '1234567890.')
     domid=$(xe vm-list name-label="$GUEST_NAME" params=dom-id minimal=true)
     port=$(xenstore-read /local/domain/$domid/console/vnc-port)
-    echo "vncviewer -via $mgmt_ip localhost:${port:2}"
+    echo "vncviewer -via root@$mgmt_ip localhost:${port:2}"
     while true
     do
         state=$(xe_min vm-list name-label="$GUEST_NAME" power-state=halted)