text: Title: More concise reports on network & config errors
  Body: If there are e.g. connection errors, then the report is quite meh:
  
  ```
  ==================================== ERRORS ====================================
  _______________________________ GET /api/failure _______________________________
  requests.exceptions.ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=1): Max retries exceeded with url: /api/failure (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f23fb0c4890>: Failed to establish a new connection: [Errno 111] Connection refused'))
  requests.exceptions.ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=1): Max retries exceeded with url: /api/failure (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f23fb0953d0>: Failed to establish a new connection: [Errno 111] Connection refused'))
  _______________________________ GET /api/success _______________________________
  requests.exceptions.ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=1): Max retries exceeded with url: /api/success (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f23fb05f710>: Failed to establish a new connection: [Errno 111] Connection refused'))
  requests.exceptions.ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=1): Max retries exceeded with url: /api/success (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f23fb244d90>: Failed to establish a new connection: [Errno 111] Connection refused'))
  Add this option to your command line parameters to see full tracebacks: --show-errors-tracebacks
  
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  =================================== SUMMARY ====================================
  ```
  
  I could be much more concise. Similarly, errors like `SerializationNotPossible` could be much better too