PR663 Added plaintext test to benchmark_config

luminus/benchmark_config

@@ -7,6 +7,7 @@
       "db_url": "/luminus/db",
       "query_url": "/luminus/db/",
       "fortune_url": "/luminus/fortune",
+      "plaintext_url": "/luminus/plaintext",
       "port": 8080,
       "approach": "Realistic",
       "classification": "Micro",