[SPARK-19505][PYTHON] AttributeError on Exception.message in Python3

## What changes were proposed in this pull request?

Added `util._message_exception` helper to use `str(e)` when `e.message` is unavailable (Python3).  Grepped for all occurrences of `.message` in `pyspark/` and these were the only occurrences.

## How was this patch tested?

- Doctests for helper function

## Legal

This is my original work and I license the work to the project under the project’s open source license.

Author: David Gingrich <david@textio.com>

Closes #16845 from dgingrich/topic-spark-19505-py3-exceptions.

1 files changed, 1 insertions, 0 deletions

diff --git a/dev/sparktestsupport/modules.py b/dev/sparktestsupport/modules.py
index 246f5188a5..78b5b8b0f4 100644
--- a/dev/sparktestsupport/modules.py
+++ b/dev/sparktestsupport/modules.py
@@ -340,6 +340,7 @@ pyspark_core = Module(
         "pyspark.profiler",
         "pyspark.shuffle",
         "pyspark.tests",
+        "pyspark.util",
     ]
 )