Show invalid XML on ExpatError

[mfeurer]

Description

Sometimes, the server returns an invalid XML which cannot be parsed by xmltodict. It would be great to see this invalid XML.

Steps/Code to Reproduce

Continuously run the unittests under high load.

Expected Results

A useful exception containing the invalid XML.

Actual Results

/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/xmltodict.py:327: ExpatError

[anisha-04]

I am working on this. I will update the current HTTP client so malformed server XML raises a useful OpenML error containing the response status and body, and add deterministic regression tests.