Fix block hotplug script locking

Do not let hotplug script inherit lock FD - if it starts some long
running process (like xenstore-watch), it will hold the lock and block other scripts.

dispvm/block.qubes

@@ -50,7 +50,7 @@ export PATH="/sbin:/bin:/usr/bin:/usr/sbin:$PATH"
 
 XENBUS_PATH="${XENBUS_PATH:?}"
 if ! [ "$1" = "add" ] || ! [ -f /var/run/qubes/fast-block-attach ] ; then
-	exec flock /var/run/qubes/hotplug-block /etc/xen/scripts/block "$@"
+	exec flock -o /var/run/qubes/hotplug-block /etc/xen/scripts/block "$@"
 fi
 
 ORIG_ARGS="$@"