Improve devstack docs for Xenserver

Minor fixes to scripts

Fixes bug 943508

Change-Id: Iaf12b9d67efa78623e8253599010f60192b4af64
diff --git a/tools/xen/prepare_dom0.sh b/tools/xen/prepare_dom0.sh
index d28a07f..b94a421 100755
--- a/tools/xen/prepare_dom0.sh
+++ b/tools/xen/prepare_dom0.sh
@@ -34,3 +34,8 @@
     make install
 fi
 
+# Clone devstack
+DEVSTACK=${DEVSTACKROOT:/root/devstack}
+if [ ! -d $DEVSTACK ]; then
+    git clone git://github.com/openstack-dev/devstack.git $DEVSTACK
+fi