Switch to message_id in find to fix the test.

examples/pipeline/in_to_out/check_linux.sh

@@ -52,7 +52,7 @@ cat out
 cat out | grep "Processed 3 file(s)"
 cat out | grep "Sent 3 file(s)"
 
-echo "db.data_default.find({"_id":1})" | mongo ${outdatabase_name} | tee /dev/stderr | grep file1_${data_source_out}
+echo "db.data_default.find({"message_id":1})" | mongo ${outdatabase_name} | tee /dev/stderr | grep file1_${data_source_out}
 
 cat ${receiver_folder}/processed/file1_${data_source_out} | grep hello1
 cat ${receiver_folder}/processed/file2_${data_source_out} | grep hello2