Changed the minScore comparator from > to >=

Closes #4303
Added simple test for minScore
trimmed down SimpleQueryTests + more assertAcked
NullPointerException in FsTranslog when reverting transient log
This happens when reverting the trans transaction log on failure, and when that happens, actually we might have failed on the transient translog creation to being with....
fixes #4223
added assertions for shard failures in stats agg tests
added more assertions to aggs tests