fix ReID trainer bugs

tools/train.py

@@ -22,9 +22,13 @@ sys.path.append(os.path.abspath(os.path.join(__dir__, '../')))
 
 from ppcls.utils import config
 from ppcls.engine.trainer import Trainer
+from ppcls.engine.trainer_reid import TrainerReID
 
 if __name__ == "__main__":
     args = config.parse_args()
     config = config.get_config(args.config, overrides=args.override, show=True)
-    trainer = Trainer(config, mode="train")
+    if "Trainer" in config:
+        trainer = eval(config["Trainer"]["name"])(config, mode="train")
+    else:
+        trainer = Trainer(config, mode="train")
     trainer.train()