Comment 6 for bug 1571616

trace from comment #4:
  File "tempest/lib/services/compute/servers_client.py", line 67, in create_server
    resp, body = self.post('servers', post_body)
  File "tempest/lib/common/rest_client.py", line 259, in post
    return self.request('POST', url, extra_headers, headers, body)
  File "tempest/lib/services/compute/base_compute_client.py", line 53, in request
    method, url, extra_headers, headers, body)
  File "tempest/lib/common/rest_client.py", line 641, in request
    resp, resp_body)
  File "tempest/lib/common/rest_client.py", line 699, in _error_checker
    raise exceptions.BadRequest(resp_body, resp=resp)
tempest.lib.exceptions.BadRequest: Bad request
Details: {u'message': u"Invalid input for field/attribute flavorRef. Value: . u'' is too short", u'code': 400}

looks like wrong parameters were passed to nova client