bug 986401: xe vm-shutdown expects running instances in os_install_domU.sh

do not fail if the instance is already halted.

Change-Id: Id080535c1eb008c9fc7335c9004318bbfb41e1f7
diff --git a/tools/xen/install_os_domU.sh b/tools/xen/install_os_domU.sh
index 54c93c7..3c25d4a 100755
--- a/tools/xen/install_os_domU.sh
+++ b/tools/xen/install_os_domU.sh
@@ -150,7 +150,7 @@
     for uuid in `xe vm-list | grep -1 instance | grep uuid | sed "s/.*\: //g"`; do
         echo "Shutting down nova instance $uuid"
         xe vm-unpause uuid=$uuid || true
-        xe vm-shutdown uuid=$uuid
+        xe vm-shutdown uuid=$uuid || true
         xe vm-destroy uuid=$uuid
     done