[skip ci] adding gpu config settings

ml-agents/mlagents/tf_utils/tf.py

 # Everywhere else is caught by the banned-modules setting for flake8
 import tensorflow as tf  # noqa I201
 from distutils.version import LooseVersion
+import horovod.tensorflow as hvd
 
 
 # LooseVersion handles things "1.2.3a" or "4.5.6-rc7" fairly sensibly.
     """
     config = tf.ConfigProto()
     config.gpu_options.allow_growth = True
+    config.gpu_options.visible_device_list = str(hvd.local_rank())
     # For multi-GPU training, set allow_soft_placement to True to allow
     # placing the operation into an alternative device automatically
     # to prevent from exceptions if the device doesn't suppport the operation

ml-agents/mlagents/trainers/stats.py

             stats_summary = values["Environment/Cumulative Reward"]
             rank = hvd.rank()
             logger.info(
-                "Horovod Rank: {}."
+                "Horovod Rank: {}. "
                 "{}: Step: {}. "
                 "Time Elapsed: {:0.3f} s "
                 "Mean "