fix split_workloads.rebalance-many-rows collision
fix split_workloads.rebalance-many-rows collision

over-the-shoulder by @danielmewes

mbroadst/rethinkdb,bchavez/rethinkdb,bchavez/rethinkdb,mbroadst/rethinkdb,robertjpayne/rethinkdb,eliangidoni/rethinkdb,jmptrader/rethinkdb,jmptrader/rethinkdb,JackieXie168/rethinkdb,jmptrader/rethinkdb,bchavez/rethinkdb,catroot/rethinkdb,bpradipt/rethinkdb,eliangidoni/rethinkdb,catroot/rethinkdb,eliangidoni/rethinkdb,jmptrader/rethinkdb,bchavez/rethinkdb,bpradipt/rethinkdb,JackieXie168/rethinkdb,eliangidoni/rethinkdb,mbroadst/rethinkdb,robertjpayne/rethinkdb,grandquista/rethinkdb,robertjpayne/rethinkdb,robertjpayne/rethinkdb,bpradipt/rethinkdb,jmptrader/rethinkdb,grandquista/rethinkdb,robertjpayne/rethinkdb,bpradipt/rethinkdb,bpradipt/rethinkdb,jmptrader/rethinkdb,bchavez/rethinkdb,catroot/rethinkdb,eliangidoni/rethinkdb,eliangidoni/rethinkdb,mbroadst/rethinkdb,grandquista/rethinkdb,JackieXie168/rethinkdb,eliangidoni/rethinkdb,mbroadst/rethinkdb,JackieXie168/rethinkdb,catroot/rethinkdb,jmptrader/rethinkdb,robertjpayne/rethinkdb,robertjpayne/rethinkdb,bchavez/rethinkdb,JackieXie168/rethinkdb,grandquista/rethinkdb,catroot/rethinkdb,JackieXie168/rethinkdb,eliangidoni/rethinkdb,catroot/rethinkdb,catroot/rethinkdb,mbroadst/rethinkdb,grandquista/rethinkdb,bpradipt/rethinkdb,JackieXie168/rethinkdb,grandquista/rethinkdb,grandquista/rethinkdb,mbroadst/rethinkdb,jmptrader/rethinkdb,robertjpayne/rethinkdb,JackieXie168/rethinkdb,bchavez/rethinkdb,mbroadst/rethinkdb,JackieXie168/rethinkdb,grandquista/rethinkdb,grandquista/rethinkdb,bpradipt/rethinkdb,robertjpayne/rethinkdb,bpradipt/rethinkdb,bchavez/rethinkdb,catroot/rethinkdb,bchavez/rethinkdb,mbroadst/rethinkdb,eliangidoni/rethinkdb,bpradipt/rethinkdb