process hangs when getting errors from couchdb

If there's a temporary problem with httpd or couchdb, the build job may hang in some cases (e.g. while exiting for an unhandled exception).

The stack trace we got in one of those cases was:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib64/python2.7/threading.py", line 812, in __bootstrap_inner
    self.run()
  File "/usr/lib64/python2.7/threading.py", line 765, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/LbNightlyTools/Utils.py", line 525, in worker
    action(*args, **kwargs)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/LbNightlyTools/Scripts/Common.py", line 679, in send
    receiver.accept(msg)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/LbNightlyTools/Scripts/Common.py", line 498, in accept
    self.project_build_completed(msg)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/LbNightlyTools/Scripts/Common.py", line 439, in project_build_completed
    self.dashboard.update(self.doc_name, data)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/LbNightlyTools/Utils.py", line 487, in update
    self.db[key] = new
  File "/workspace/venv/centos7/lib/python2.7/site-packages/couchdb/client.py", line 447, in __setitem__
    status, headers, data = resource.put_json(body=content)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/couchdb/http.py", line 578, in put_json
    **params)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/couchdb/http.py", line 596, in _request_json
    headers=headers, **params)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/couchdb/http.py", line 592, in _request
    credentials=self.credentials)
  File "/workspace/venv/centos7/lib/python2.7/site-packages/couchdb/http.py", line 429, in request
    raise ServerError((status, error))
ServerError: (500, (u'unknown_error', u'undefined'))