refine build strategy for the model optimize test=develop (#3435)

* refine build strategy for the model optimize test=develop

* fix according develop test=develop

tools/train.py

@@ -158,6 +158,7 @@ def main():
     # compile program for multi-devices
     build_strategy = fluid.BuildStrategy()
     build_strategy.fuse_all_optimizer_ops = False
+    build_strategy.fuse_elewise_add_act_ops = True
     # only enable sync_bn in multi GPU devices
     sync_bn = getattr(model.backbone, 'norm_type', None) == 'sync_bn'
     build_strategy.sync_batch_norm = sync_bn and devices_num > 1 \