Make the standard devstack logging work with XenServer

Fixes bug 1087387

Stop redirecting the output in devstack to ensure when
you configure LOGFILE that the devstack scripts keep working

Change-Id: I00dce315f5f79c4fc351d9ab11c504274d998fce
diff --git a/tools/xen/build_xva.sh b/tools/xen/build_xva.sh
index 9eae190..c359c55 100755
--- a/tools/xen/build_xva.sh
+++ b/tools/xen/build_xva.sh
@@ -66,7 +66,7 @@
 # network restart required for getting the right gateway
 /etc/init.d/networking restart
 chown -R stack /opt/stack
-su -c "/opt/stack/run.sh > /opt/stack/run.sh.log 2>&1" stack
+su -c "/opt/stack/run.sh > /opt/stack/run.sh.log" stack
 exit 0
 EOF