Use multiple rescores to apply script scoring

This should spit out almost exactly the same results but has the following
advantages:
1.  Script score is never applied to more then 8192 documents per shard.
2.  Script score isn't calculated twice for the phrase rescore.

This helps for searches that have a phrase rescore and find a ton of matches.
Mostly that is searches on large wikis for two common words.

Bug: 60151
Change-Id: I20f312a4b7c76b82e9e79970f5f835df20298763
Merge "Use multiple rescores to apply script scoring"