Further clean up of error messages

[gordonwatts]

PR #378 was working but not tuned up before the submission. This PR:

• Improves error logic (it wasn't wrong before, just two options for a branch)
• Improves the error message further.

Error message now looks like the following:

  File "/venv/lib/python3.9/site-packages/servicex/dataset_group.py", line 76, in as_signed_urls_async
    return await asyncio.gather(*self.tasks)
  File "/venv/lib/python3.9/site-packages/servicex/query.py", line 521, in as_signed_urls_async
    return await self.submit_and_download(
  File "/venv/lib/python3.9/site-packages/servicex/query.py", line 260, in submit_and_download
    self.request_id = await self.servicex.submit_transform(sx_request)
  File "/venv/lib/python3.9/site-packages/servicex/servicex_adapter.py", line 120, in submit_transform
    raise RuntimeError("ServiceX WebAPI Error during transformation "
RuntimeError: ServiceX WebAPI Error during transformation submission: 504 - <Response [504 Gateway Time-out]>

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 73.85%. Comparing base (e015c93) to head (7191e4e).

Files	Patch %	Lines
servicex/servicex_adapter.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           3.0_develop     #379      +/-   ##
===============================================
- Coverage        73.88%   73.85%   -0.04%     
===============================================
  Files               42       42              
  Lines             2309     2310       +1     
===============================================
  Hits              1706     1706              
- Misses             603      604       +1     

Flag	Coverage Δ
unittests	73.85% <66.66%> (-0.04%)	⬇️

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[BenGalewsky]

Even better