Open other clusters' config in foreign mode

Signed-off-by: Stephen Shirley <diamond@google.com>
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

tools/cluster-merge

@@ -263,7 +263,7 @@ class Merger(object):
     fake_ec_id = 0 # Needs to be uniq over the whole config merge
 
     for data in self.merger_data:
-      other_config = config.ConfigWriter(data.config_path)
+      other_config = config.ConfigWriter(data.config_path, accept_foreign=True)
 
       for node in other_config.GetNodeList():
         node_info = other_config.GetNodeInfo(node)