Tf2 test fixups (#5391)

* Fix oversight in importing tf.compat.v1 as tf.

* Actually disable test for lstm in TF2.1

Since the testing framework actually uses pytest, the version
check needs to be moved.

tests/python/frontend/tensorflow/test_bn_dynamic.py

@@ -22,7 +22,10 @@ in TensorFlow frontend when mean and variance are not given.
 """
 import tvm
 import numpy as np
-import tensorflow as tf
+try:
+    import tensorflow.compat.v1 as tf
+except ImportError:
+    import tensorflow as tf
 from tvm import relay
 from tensorflow.python.framework import graph_util
 

tests/python/frontend/tensorflow/test_forward.py

@@ -1901,6 +1901,8 @@ def _test_lstm_cell(batch_size, num_hidden, num_layers, forget_bias, dtype):
 
 def test_forward_lstm():
     '''test LSTM block cell'''
+    if package_version.parse(tf.VERSION) < package_version.parse('2.0.0'):
+        #in 2.0, tf.contrib.rnn.LSTMBlockCell is removed
         _test_lstm_cell(1, 2, 1, 0.5, 'float32')
 
 
@@ -3308,8 +3310,6 @@ if __name__ == '__main__':
     test_forward_ptb()
 
     # RNN
-    if package_version.parse(tf.VERSION) < package_version.parse('2.0.0'):
-        #in 2.0, tf.contrib.rnn.LSTMBlockCell is removed
     test_forward_lstm()
 
     # Elementwise