Add MODEL_VARIABLES in SyncBN (fix #1270)

tensorpack/models/batch_norm.py

@@ -37,6 +37,10 @@ def get_bn_variables(n_out, use_scale, use_bias, beta_init, gamma_init):
                                   initializer=tf.constant_initializer(), trainable=False)
     moving_var = tf.get_variable('variance/EMA', [n_out],
                                  initializer=tf.constant_initializer(1.0), trainable=False)
+
+    if get_current_tower_context().is_main_training_tower:
+        for v in [moving_mean, moving_var]:
+            tf.add_to_collection(tf.GraphKeys.MODEL_VARIABLES, v)
     return beta, gamma, moving_mean, moving_var