Tf2 test fixups (apache#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 @@
 """
 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

@@ -1901,7 +1901,9 @@ def _get_tensorflow_output():
 
 def test_forward_lstm():
     '''test LSTM block cell'''
-    _test_lstm_cell(1, 2, 1, 0.5, 'float32')
+    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')
 
 
 #######################################################################
@@ -3308,9 +3310,7 @@ def test_forward_isfinite():
     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()
+    test_forward_lstm()
 
     # Elementwise
     test_forward_ceil()