Fix the watcher with down nodes

The watcher didn't handle the down nodes, fix this by ignoring (in
secondary node reboot checks) any node that doesn't return a boot id.

Reviewed-by: imsnah

daemons/ganeti-watcher

@@ -306,6 +306,11 @@ class Watcher(object):
     check_nodes = []
     for name, new_id in self.bootids.iteritems():
       old = notepad.GetNodeBootID(name)
+      if new_id is None:
+        # Bad node, not returning a boot id
+        logging.debug("Node %s missing boot id, skipping secondary checks",
+                      name)
+        continue
       if old != new_id:
         # Node's boot ID has changed, proably through a reboot.
         check_nodes.append(name)