disable tensorflow warnings by default (#2931)

ml-agents/mlagents/tf_utils/__init__.py

 from mlagents.tf_utils.tf import tf as tf  # noqa
+from mlagents.tf_utils.tf import set_warnings_enabled  # noqa

ml-agents/mlagents/tf_utils/tf.py

     import tensorflow.compat.v1 as tf
 
     tf.disable_v2_behavior()
+    tf_logging = tf.logging
-    pass
+    try:
+        # Newer versions of tf 1.x will complain that tf.logging is deprecated
+        tf_logging = tf.compat.v1.logging
+    except AttributeError:
+        # Fall back to the safe import, even if it might generate a warning or two.
+        tf_logging = tf.logging
+
+
+def set_warnings_enabled(is_enabled: bool) -> None:
+    """
+    Enable or disable tensorflow warnings (notabley, this disables deprecation warnings.
+    :param is_enabled:
+    """
+    level = tf_logging.WARN if is_enabled else tf_logging.ERROR
+    tf_logging.set_verbosity(level)

ml-agents/mlagents/trainers/learn.py

 
 from typing import Any, Callable, Optional, List, NamedTuple
 
-
+from mlagents import tf_utils
 from mlagents.trainers.trainer_controller import TrainerController
 from mlagents.trainers.exception import TrainerError
 from mlagents.trainers.meta_curriculum import MetaCurriculum
     if options.debug:
         trainer_logger.setLevel("DEBUG")
         env_logger.setLevel("DEBUG")
+    else:
+        # disable noisy warnings from tensorflow.
+        tf_utils.set_warnings_enabled(False)
     if options.env_path is None and options.num_runs > 1:
         raise TrainerError(
             "It is not possible to launch more than one concurrent training session "