Fix undefined names in Python code (microsoft#599)

* Update pytorch_tabnet.py

$ `flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics`
```
./qlib/qlib/contrib/model/pytorch_tabnet.py:567:38: F821 undefined name 'inp'
            self.independ.append(GLU(inp, out_dim, vbs=vbs))
                                     ^
./qlib/examples/model_rolling/task_manager_rolling.py:75:18: F821 undefined name 'task_train'
        run_task(task_train, self.task_pool, experiment_name=self.experiment_name)
                 ^
2     F821 undefined name 'task_train'
2
```

* Fix undefined names in Python code

* from qlib.model.trainer import task_train

examples/model_rolling/task_manager_rolling.py

@@ -17,7 +17,7 @@
 from qlib.workflow.task.manage import TaskManager, run_task
 from qlib.workflow.task.collect import RecorderCollector
 from qlib.model.ens.group import RollingGroup
-from qlib.model.trainer import TrainerRM
+from qlib.model.trainer import TrainerRM, task_train
 from qlib.tests.config import CSI100_RECORD_LGB_TASK_CONFIG, CSI100_RECORD_XGBOOST_TASK_CONFIG
 
 

qlib/contrib/model/pytorch_tabnet.py

@@ -564,7 +564,7 @@ def __init__(self, inp_dim, out_dim, shared, n_ind, vbs):
             self.shared = None
         self.independ = nn.ModuleList()
         if first:
-            self.independ.append(GLU(inp, out_dim, vbs=vbs))
+            self.independ.append(GLU(inp_dim, out_dim, vbs=vbs))
         for x in range(first, n_ind):
             self.independ.append(GLU(out_dim, out_dim, vbs=vbs))
         self.scale = float(np.sqrt(0.5))