Improve error message in case of Solr error

When indexing a file where e.g. Tika extracts too long meta data entries, the current exception handling for the resulting HTTP 400 error from solr is not very helpful.

open-semantic-etl/src/opensemanticetl/export_solr.py

Line 156 in f51efea

r.raise_for_status()

Printing the response text in addition makes it far more understandable where the issue comes from.
So I would propose to add a print statement in case of status_code >= 400

 # if bad status code, raise exception
  if r.status_code >= 400:
      print('Solr {} error: {}'.format(r.status_code, r.text))
  r.raise_for_status()

See the previous error output:

Error while posting data to Solr: 400 Client Error: Bad Request for url: http://localhost:8983/solr/opensemanticsearch/update?commit=trueError while exporting to index or database: /media/text_document.docx

vs. the new error output:

"msg":"Exception writing document id /media/text_document.docx to the index; possible analysis error: Document contains at least one immense term in field="Text_TextEntry_ss" (whose UTF8 encoding is longer than the max length 32766), all of which were skipped. Please correct the analyzer to not produce such terms. The prefix of the first immense term is: '[107, 101, 121, 119, 111, 114, 100, 61, 88, 77, 76, 58, 99, 111, 109, 46, 97, 100, 111, 98, 101, 46, 120, 109, 112, 44, 32, 118, 97, 108]...', original message: bytes can be at most 32766 in length; got 38935. Perhaps the document has an indexed string field (solr.StrField) which is too large",
"code":400}}