Drop unused variable when post-processing results

original_results is not used in either method, and can be safely removed.
ignore 400 (index already exists) when creating an index in Elasticsearch
404 when initially retrieving mappings is ok
Merge pull request #1032 from maikhoepfel/patch-1

Drop unused variable when post-processing results
RelatedSearchQuerySet: move class globals to instance properties

This caused obvious failures in the test suite and presumably
elsewhere when multiple RelatedSearchQuerySet instances were in use