Print the driver stdout/stderr if we fail to decode it in jenkins. (#567

)

* Print the driver stdout/stderr if we fail to decode it in jenkins.

* Fix whitespace.

* Add explanation.

test/jenkins_tests/multi_node_docker_test.py

@@ -20,10 +20,25 @@ def wait_for_output(proc):
     A tuple of the stdout and stderr of the process as strings.
   """
   stdout_data, stderr_data = proc.communicate()
-  stdout_data = (stdout_data.decode("ascii") if stdout_data is not None
-                 else None)
-  stderr_data = (stderr_data.decode("ascii") if stderr_data is not None
-                 else None)
+
+  if stdout_data is not None:
+    try:
+      # NOTE(rkn): This try/except block is here because I once saw an
+      # exception raised here and want to print more information if that
+      # happens again.
+      stdout_data = stdout_data.decode("ascii")
+    except UnicodeDecodeError:
+      raise Exception("Failed to decode stdout_data:", stdout_data)
+
+  if stderr_data is not None:
+    try:
+      # NOTE(rkn): This try/except block is here because I once saw an
+      # exception raised here and want to print more information if that
+      # happens again.
+      stderr_data = stderr_data.decode("ascii")
+    except UnicodeDecodeError:
+      raise Exception("Failed to decode stderr_data:", stderr_data)
+
   return stdout_data, stderr_data