Load nccl so (fix #913)

tensorpack/models/batch_norm.py

@@ -227,6 +227,12 @@ def BatchNorm(inputs, axis=None, training=None, momentum=0.9, epsilon=1e-5,
                     "Cross-GPU BatchNorm is only supported in TF>=1.10 ." \
                     "Upgrade TF or apply this patch manually: https://github.com/tensorflow/tensorflow/pull/20360"
 
+                try:
+                    from tensorflow.contrib.nccl.python.ops.nccl_ops import _validate_and_load_nccl_so
+                except Exception:
+                    pass
+                else:
+                    _validate_and_load_nccl_so()
                 from tensorflow.contrib.nccl.ops import gen_nccl_ops
                 shared_name = re.sub('tower[0-9]+/', '', tf.get_variable_scope().name)
                 batch_mean = gen_nccl_ops.nccl_all_reduce(