Make TF graph seed deterministic

ml-agents/mlagents/trainers/common/nn_policy.py

         Builds the tensorflow graph needed for this policy.
         """
         with self.graph.as_default():
+            tf.set_random_seed(self.seed)
             _vars = tf.get_collection(tf.GraphKeys.GLOBAL_VARIABLES)
             if len(_vars) > 0:
                 # We assume the first thing created in the graph is the Policy. If

ml-agents/mlagents/trainers/tf_policy.py

         self.sess = tf.Session(
             config=tf_utils.generate_session_config(), graph=self.graph
         )
-        tf.set_random_seed(seed)
+        self.seed = seed
         if self.use_recurrent:
             self.m_size = trainer_parameters["memory_size"]
             self.sequence_length = trainer_parameters["sequence_length"]