Fix unit test stability with testing job name generation (#248)

Since the job name generation depends on timestamps being unique,
if the two names were generated quickly enough, the names could end
up being the same despite the code's logic being correct. Adding a
sleep statement in the test should fix this.

Author: laurenyu

tests/unit/test_estimator.py

@@ -15,6 +15,7 @@
 import logging
 import json
 import os
+from time import sleep
 
 import pytest
 from mock import Mock, patch
@@ -386,6 +387,7 @@ def test_prepare_for_training_unique_job_name_generation(sagemaker_session):
     fw._prepare_for_training()
     first_job_name = fw._current_job_name
 
+    sleep(0.1)
     fw._prepare_for_training()
     second_job_name = fw._current_job_name