xenapi: display IP and DevStack result on console

The devstack setup service can update /etc/issue, displaying the status
of the installation and the VM's management IP. With this change, after
the devstack service finsihed, the login prompt will look like this:

OpenStack VM - Installed by DevStack
  Management IP:   10.219.3.108
  Devstack run:    SUCCEEDED

DevStackOSDomU login:

This helps people to log in to their system.

Change-Id: Idd6bbd5faf9ced5618cd3e95191bfc3b89473fa2

tools/xen/build_xva.sh

@@ -119,6 +119,20 @@ script
     if su -c "/opt/stack/run.sh" $STACK_USER; then
         touch /var/run/devstack.succeeded
     fi
+
+    # Update /etc/issue
+    {
+        echo "OpenStack VM - Installed by DevStack"
+        IPADDR=\$(ip -4 address show eth0 | sed -n 's/.*inet \\([0-9\.]\\+\\).*/\1/p')
+        echo "  Management IP:   \$IPADDR"
+        echo -n "  Devstack run:    "
+        if [ -e /var/run/devstack.succeeded ]; then
+            echo "SUCCEEDED"
+        else
+            echo "FAILED"
+        fi
+        echo ""
+    } > /etc/issue
     initctl start hvc0 > /dev/null 2>&1
 end script
 EOF