SG-35087 Stop masking exceptions

[carlos-villavicencio-adsk]

Sometimes we have support cases with messages like:

[33532 DEBUG sgtk.core.descriptor.io_descriptor.appstore] ...could not establish connection: 'SSLCertVerificationError' object has no attribute 'message'

File "C:\Users\xxxxxxxx\cfg\install\core\scripts\tank_cmd.py", line 1494, in run_engine_cmd
'"tank unregister_folders /path/to/folder"' % exc.message
AttributeError: 'TankInitError' object has no attribute 'message'

Turns out tk-core is raising an error the moment the error is handled.  This PR attempts to fix this by gracefully getting the error description.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.44%. Comparing base (11d3cd7) to head (c9ad299).

:exclamation: Current head c9ad299 differs from pull request most recent head b8fc2a1. Consider uploading reports for the commit b8fc2a1 to get more accurate results

Files	Patch %	Lines
python/tank/descriptor/io_descriptor/appstore.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #968 +/- ## ========================================== - Coverage 79.45% 79.44% -0.01% ========================================== Files 199 199 Lines 20856 20858 +2 ========================================== Hits 16571 16571 - Misses 4285 4287 +2 ```

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[carlos-villavicencio-adsk]

I cannot make codecov happy even adding the test it wanted 😢

[carlos-villavicencio-adsk]

@julien-lang Seems like a Py2 Py3 problem. It seems like we were relying on httpllib2 on Py2. I tried using getattr but we might end up losing the error message.