Clean up naming of variables in rule key calculation
Clean up naming of variables in rule key calculation

Summary:
Use separate variables for the future we get from the cache and the one
we calculate ourselves.  Just makes dataflow clearer, IMO.

Test Plan: CI

Reviewed By: andrewjcg

fbshipit-source-id: 1be60e1

vschs007/buck,SeleniumHQ/buck,marcinkwiatkowski/buck,JoelMarcey/buck,romanoid/buck,zhan-xiong/buck,Addepar/buck,robbertvanginkel/buck,dsyang/buck,rmaz/buck,JoelMarcey/buck,dsyang/buck,shybovycha/buck,clonetwin26/buck,Addepar/buck,marcinkwiatkowski/buck,k21/buck,marcinkwiatkowski/buck,ilya-klyuchnikov/buck,marcinkwiatkowski/buck,SeleniumHQ/buck,Addepar/buck,vschs007/buck,brettwooldridge/buck,LegNeato/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,nguyentruongtho/buck,shybovycha/buck,romanoid/buck,vschs007/buck,rmaz/buck,facebook/buck,facebook/buck,JoelMarcey/buck,zhan-xiong/buck,vschs007/buck,facebook/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,LegNeato/buck,LegNeato/buck,vschs007/buck,JoelMarcey/buck,k21/buck,zpao/buck,robbertvanginkel/buck,rmaz/buck,kageiit/buck,clonetwin26/buck,SeleniumHQ/buck,shs96c/buck,shybovycha/buck,marcinkwiatkowski/buck,robbertvanginkel/buck,brettwooldridge/buck,ilya-klyuchnikov/buck,zpao/buck,ilya-klyuchnikov/buck,ilya-klyuchnikov/buck,clonetwin26/buck,vschs007/buck,dsyang/buck,k21/buck,marcinkwiatkowski/buck,rmaz/buck,SeleniumHQ/buck,SeleniumHQ/buck,k21/buck,SeleniumHQ/buck,ilya-klyuchnikov/buck,k21/buck,dsyang/buck,clonetwin26/buck,kageiit/buck,shs96c/buck,ilya-klyuchnikov/buck,zpao/buck,robbertvanginkel/buck,rmaz/buck,vschs007/buck,robbertvanginkel/buck,shs96c/buck,Addepar/buck,romanoid/buck,brettwooldridge/buck,brettwooldridge/buck,kageiit/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,kageiit/buck,rmaz/buck,shybovycha/buck,clonetwin26/buck,brettwooldridge/buck,clonetwin26/buck,LegNeato/buck,romanoid/buck,marcinkwiatkowski/buck,rmaz/buck,vschs007/buck,facebook/buck,dsyang/buck,shybovycha/buck,Addepar/buck,dsyang/buck,LegNeato/buck,romanoid/buck,ilya-klyuchnikov/buck,shs96c/buck,Addepar/buck,JoelMarcey/buck,rmaz/buck,JoelMarcey/buck,vschs007/buck,clonetwin26/buck,marcinkwiatkowski/buck,SeleniumHQ/buck,clonetwin26/buck,k21/buck,brettwooldridge/buck,ilya-klyuchnikov/buck,shybovycha/buck,dsyang/buck,zhan-xiong/buck,dsyang/buck,k21/buck,romanoid/buck,shybovycha/buck,LegNeato/buck,marcinkwiatkowski/buck,shs96c/buck,JoelMarcey/buck,clonetwin26/buck,romanoid/buck,dsyang/buck,k21/buck,clonetwin26/buck,zhan-xiong/buck,shs96c/buck,Addepar/buck,brettwooldridge/buck,nguyentruongtho/buck,Addepar/buck,SeleniumHQ/buck,kageiit/buck,zpao/buck,dsyang/buck,vschs007/buck,facebook/buck,shs96c/buck,Addepar/buck,zhan-xiong/buck,shybovycha/buck,shybovycha/buck,nguyentruongtho/buck,brettwooldridge/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,ilya-klyuchnikov/buck,nguyentruongtho/buck,k21/buck,nguyentruongtho/buck,shs96c/buck,kageiit/buck,zhan-xiong/buck,JoelMarcey/buck,robbertvanginkel/buck,romanoid/buck,brettwooldridge/buck,vschs007/buck,facebook/buck,JoelMarcey/buck,Addepar/buck,JoelMarcey/buck,robbertvanginkel/buck,romanoid/buck,LegNeato/buck,LegNeato/buck,nguyentruongtho/buck,facebook/buck,zhan-xiong/buck,vschs007/buck,nguyentruongtho/buck,marcinkwiatkowski/buck,JoelMarcey/buck,romanoid/buck,zhan-xiong/buck,shs96c/buck,shs96c/buck,SeleniumHQ/buck,robbertvanginkel/buck,robbertvanginkel/buck,clonetwin26/buck,JoelMarcey/buck,LegNeato/buck,k21/buck,zpao/buck,robbertvanginkel/buck,LegNeato/buck,shs96c/buck,brettwooldridge/buck,shs96c/buck,marcinkwiatkowski/buck,shybovycha/buck,k21/buck,shybovycha/buck,shybovycha/buck,SeleniumHQ/buck,shybovycha/buck,rmaz/buck,LegNeato/buck,k21/buck,zhan-xiong/buck,brettwooldridge/buck,brettwooldridge/buck,kageiit/buck,romanoid/buck,dsyang/buck,rmaz/buck,rmaz/buck,brettwooldridge/buck,romanoid/buck,dsyang/buck,shs96c/buck,rmaz/buck,SeleniumHQ/buck,clonetwin26/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,zhan-xiong/buck,vschs007/buck,zhan-xiong/buck,dsyang/buck,JoelMarcey/buck,zpao/buck,LegNeato/buck,LegNeato/buck,clonetwin26/buck,Addepar/buck,k21/buck,zhan-xiong/buck,Addepar/buck,romanoid/buck,zhan-xiong/buck,rmaz/buck,zpao/buck,marcinkwiatkowski/buck,Addepar/buck