Use a dedicated cluster name for GeoDistanceSearchBenchmark (like we do for other benchmarks).
Remove 'term_index_interval' and 'term_index_divisor'

These settings are no longer relevant since they are codec /
postingsformat level settings since Lucene 4.0

Closes #3912
Fix bug in explain for function_score queries.

The explain output for function_score queries with score_mode=max or
score_mode=min was incorrect, returning instead the value of the last
function.  This change fixes this.