CachingBuildEngine: only get output size/hash when building locally
CachingBuildEngine: only get output size/hash when building locally

Summary:
This can get pretty expensive, and we only really care when building
locally.

Test Plan: ran tests

marcinkwiatkowski/buck,davido/buck,grumpyjames/buck,janicduplessis/buck,justinmuller/buck,dsyang/buck,Learn-Android-app/buck,brettwooldridge/buck,justinmuller/buck,mogers/buck,LegNeato/buck,justinmuller/buck,LegNeato/buck,daedric/buck,brettwooldridge/buck,bocon13/buck,JoelMarcey/buck,lukw00/buck,k21/buck,siddhartharay007/buck,raviagarwal7/buck,SeleniumHQ/buck,SeleniumHQ/buck,grumpyjames/buck,Distrotech/buck,shybovycha/buck,clonetwin26/buck,Learn-Android-app/buck,shs96c/buck,rhencke/buck,brettwooldridge/buck,Addepar/buck,OkBuilds/buck,luiseduardohdbackup/buck,SeleniumHQ/buck,liuyang-li/buck,rmaz/buck,pwz3n0/buck,sdwilsh/buck,tgummerer/buck,rhencke/buck,rowillia/buck,clonetwin26/buck,1yvT0s/buck,zpao/buck,Dominator008/buck,robbertvanginkel/buck,rmaz/buck,marcinkwiatkowski/buck,robbertvanginkel/buck,pwz3n0/buck,mogers/buck,justinmuller/buck,shs96c/buck,raviagarwal7/buck,tgummerer/buck,kageiit/buck,davido/buck,stuhood/buck,zpao/buck,tgummerer/buck,bocon13/buck,SeleniumHQ/buck,pwz3n0/buck,rowillia/buck,artiya4u/buck,JoelMarcey/buck,dushmis/buck,k21/buck,shybovycha/buck,romanoid/buck,JoelMarcey/buck,rowillia/buck,janicduplessis/buck,facebook/buck,romanoid/buck,stuhood/buck,kageiit/buck,marcinkwiatkowski/buck,Learn-Android-app/buck,romanoid/buck,k21/buck,SeleniumHQ/buck,mikekap/buck,liuyang-li/buck,vine/buck,davido/buck,sdwilsh/buck,daedric/buck,SeleniumHQ/buck,justinmuller/buck,romanoid/buck,1yvT0s/buck,artiya4u/buck,facebook/buck,Dominator008/buck,clonetwin26/buck,rmaz/buck,k21/buck,liuyang-li/buck,siddhartharay007/buck,Addepar/buck,kageiit/buck,rmaz/buck,luiseduardohdbackup/buck,ilya-klyuchnikov/buck,shybovycha/buck,liuyang-li/buck,vine/buck,dsyang/buck,1yvT0s/buck,rmaz/buck,JoelMarcey/buck,bocon13/buck,daedric/buck,rhencke/buck,raviagarwal7/buck,Addepar/buck,dsyang/buck,brettwooldridge/buck,dsyang/buck,shs96c/buck,romanoid/buck,romanoid/buck,illicitonion/buck,daedric/buck,artiya4u/buck,sdwilsh/buck,dushmis/buck,Learn-Android-app/buck,daedric/buck,rowillia/buck,shybovycha/buck,davido/buck,zhan-xiong/buck,mogers/buck,SeleniumHQ/buck,sdwilsh/buck,JoelMarcey/buck,raviagarwal7/buck,dsyang/buck,siddhartharay007/buck,pwz3n0/buck,Addepar/buck,shybovycha/buck,davido/buck,Dominator008/buck,ilya-klyuchnikov/buck,ilya-klyuchnikov/buck,bocon13/buck,artiya4u/buck,kageiit/buck,nguyentruongtho/buck,pwz3n0/buck,zpao/buck,clonetwin26/buck,liuyang-li/buck,JoelMarcey/buck,davido/buck,lukw00/buck,dushmis/buck,liuyang-li/buck,rmaz/buck,SeleniumHQ/buck,zhan-xiong/buck,mogers/buck,davido/buck,ilya-klyuchnikov/buck,dushmis/buck,lukw00/buck,stuhood/buck,LegNeato/buck,illicitonion/buck,artiya4u/buck,dsyang/buck,k21/buck,darkforestzero/buck,Dominator008/buck,liuyang-li/buck,shs96c/buck,grumpyjames/buck,LegNeato/buck,bocon13/buck,artiya4u/buck,ilya-klyuchnikov/buck,k21/buck,bocon13/buck,robbertvanginkel/buck,LegNeato/buck,kageiit/buck,Learn-Android-app/buck,Dominator008/buck,illicitonion/buck,JoelMarcey/buck,ilya-klyuchnikov/buck,janicduplessis/buck,Dominator008/buck,dsyang/buck,marcinkwiatkowski/buck,tgummerer/buck,lukw00/buck,rowillia/buck,JoelMarcey/buck,stuhood/buck,Distrotech/buck,raviagarwal7/buck,nguyentruongtho/buck,mogers/buck,grumpyjames/buck,davido/buck,mogers/buck,rmaz/buck,grumpyjames/buck,rmaz/buck,marcinkwiatkowski/buck,daedric/buck,vschs007/buck,brettwooldridge/buck,vine/buck,romanoid/buck,k21/buck,brettwooldridge/buck,justinmuller/buck,facebook/buck,mogers/buck,Dominator008/buck,JoelMarcey/buck,pwz3n0/buck,stuhood/buck,LegNeato/buck,janicduplessis/buck,vschs007/buck,dsyang/buck,dushmis/buck,Addepar/buck,grumpyjames/buck,illicitonion/buck,shybovycha/buck,siddhartharay007/buck,rmaz/buck,illicitonion/buck,ilya-klyuchnikov/buck,darkforestzero/buck,lukw00/buck,robbertvanginkel/buck,clonetwin26/buck,robbertvanginkel/buck,OkBuilds/buck,marcinkwiatkowski/buck,illicitonion/buck,Learn-Android-app/buck,ilya-klyuchnikov/buck,darkforestzero/buck,Dominator008/buck,siddhartharay007/buck,Learn-Android-app/buck,brettwooldridge/buck,janicduplessis/buck,Addepar/buck,mikekap/buck,bocon13/buck,mikekap/buck,pwz3n0/buck,clonetwin26/buck,raviagarwal7/buck,stuhood/buck,dsyang/buck,artiya4u/buck,illicitonion/buck,vine/buck,rowillia/buck,raviagarwal7/buck,justinmuller/buck,Learn-Android-app/buck,vschs007/buck,nguyentruongtho/buck,marcinkwiatkowski/buck,Learn-Android-app/buck,rmaz/buck,bocon13/buck,romanoid/buck,shs96c/buck,justinmuller/buck,clonetwin26/buck,illicitonion/buck,rowillia/buck,sdwilsh/buck,OkBuilds/buck,rhencke/buck,shs96c/buck,mikekap/buck,marcinkwiatkowski/buck,darkforestzero/buck,darkforestzero/buck,zhan-xiong/buck,brettwooldridge/buck,dsyang/buck,sdwilsh/buck,dushmis/buck,clonetwin26/buck,bocon13/buck,justinmuller/buck,Dominator008/buck,marcinkwiatkowski/buck,robbertvanginkel/buck,sdwilsh/buck,luiseduardohdbackup/buck,sdwilsh/buck,vine/buck,darkforestzero/buck,JoelMarcey/buck,SeleniumHQ/buck,facebook/buck,luiseduardohdbackup/buck,ilya-klyuchnikov/buck,daedric/buck,rhencke/buck,zhan-xiong/buck,siddhartharay007/buck,SeleniumHQ/buck,tgummerer/buck,dushmis/buck,illicitonion/buck,dushmis/buck,kageiit/buck,tgummerer/buck,robbertvanginkel/buck,1yvT0s/buck,vschs007/buck,grumpyjames/buck,vschs007/buck,grumpyjames/buck,liuyang-li/buck,mogers/buck,daedric/buck,rowillia/buck,siddhartharay007/buck,ilya-klyuchnikov/buck,1yvT0s/buck,shybovycha/buck,davido/buck,LegNeato/buck,brettwooldridge/buck,Addepar/buck,k21/buck,luiseduardohdbackup/buck,Addepar/buck,OkBuilds/buck,vine/buck,rhencke/buck,grumpyjames/buck,janicduplessis/buck,dsyang/buck,pwz3n0/buck,raviagarwal7/buck,zpao/buck,shs96c/buck,justinmuller/buck,rmaz/buck,luiseduardohdbackup/buck,shybovycha/buck,Learn-Android-app/buck,rhencke/buck,grumpyjames/buck,zhan-xiong/buck,OkBuilds/buck,Distrotech/buck,luiseduardohdbackup/buck,davido/buck,nguyentruongtho/buck,OkBuilds/buck,lukw00/buck,daedric/buck,marcinkwiatkowski/buck,JoelMarcey/buck,mikekap/buck,sdwilsh/buck,Addepar/buck,artiya4u/buck,shybovycha/buck,vschs007/buck,darkforestzero/buck,vine/buck,OkBuilds/buck,janicduplessis/buck,facebook/buck,siddhartharay007/buck,vine/buck,zhan-xiong/buck,shs96c/buck,rowillia/buck,vschs007/buck,k21/buck,pwz3n0/buck,marcinkwiatkowski/buck,tgummerer/buck,marcinkwiatkowski/buck,1yvT0s/buck,davido/buck,rhencke/buck,vine/buck,kageiit/buck,daedric/buck,vschs007/buck,lukw00/buck,liuyang-li/buck,raviagarwal7/buck,stuhood/buck,mikekap/buck,Distrotech/buck,zhan-xiong/buck,brettwooldridge/buck,k21/buck,1yvT0s/buck,Distrotech/buck,Addepar/buck,vschs007/buck,tgummerer/buck,rhencke/buck,dushmis/buck,darkforestzero/buck,OkBuilds/buck,ilya-klyuchnikov/buck,shs96c/buck,zhan-xiong/buck,Distrotech/buck,mikekap/buck,raviagarwal7/buck,mikekap/buck,shs96c/buck,pwz3n0/buck,Distrotech/buck,mikekap/buck,zpao/buck,justinmuller/buck,zpao/buck,illicitonion/buck,LegNeato/buck,robbertvanginkel/buck,SeleniumHQ/buck,LegNeato/buck,SeleniumHQ/buck,Dominator008/buck,1yvT0s/buck,OkBuilds/buck,robbertvanginkel/buck,rhencke/buck,OkBuilds/buck,daedric/buck,stuhood/buck,pwz3n0/buck,vine/buck,sdwilsh/buck,robbertvanginkel/buck,shybovycha/buck,Distrotech/buck,k21/buck,Dominator008/buck,shs96c/buck,robbertvanginkel/buck,lukw00/buck,zhan-xiong/buck,raviagarwal7/buck,vschs007/buck,raviagarwal7/buck,vschs007/buck,brettwooldridge/buck,JoelMarcey/buck,darkforestzero/buck,1yvT0s/buck,rowillia/buck,OkBuilds/buck,nguyentruongtho/buck,Addepar/buck,bocon13/buck,brettwooldridge/buck,shybovycha/buck,ilya-klyuchnikov/buck,Distrotech/buck,zhan-xiong/buck,romanoid/buck,luiseduardohdbackup/buck,rowillia/buck,clonetwin26/buck,shs96c/buck,stuhood/buck,daedric/buck,illicitonion/buck,vschs007/buck,artiya4u/buck,vschs007/buck,zhan-xiong/buck,LegNeato/buck,rhencke/buck,lukw00/buck,janicduplessis/buck,justinmuller/buck,sdwilsh/buck,grumpyjames/buck,Distrotech/buck,OkBuilds/buck,davido/buck,darkforestzero/buck,sdwilsh/buck,clonetwin26/buck,darkforestzero/buck,mikekap/buck,romanoid/buck,grumpyjames/buck,luiseduardohdbackup/buck,ilya-klyuchnikov/buck,mogers/buck,liuyang-li/buck,Distrotech/buck,robbertvanginkel/buck,artiya4u/buck,zhan-xiong/buck,daedric/buck,LegNeato/buck,vine/buck,brettwooldridge/buck,k21/buck,lukw00/buck,illicitonion/buck,clonetwin26/buck,dsyang/buck,Addepar/buck,janicduplessis/buck,tgummerer/buck,janicduplessis/buck,shybovycha/buck,nguyentruongtho/buck,robbertvanginkel/buck,mogers/buck,Addepar/buck,LegNeato/buck,JoelMarcey/buck,clonetwin26/buck,mikekap/buck,facebook/buck,darkforestzero/buck,janicduplessis/buck,illicitonion/buck,lukw00/buck,marcinkwiatkowski/buck,mogers/buck,LegNeato/buck,tgummerer/buck,dushmis/buck,siddhartharay007/buck,shs96c/buck,romanoid/buck,davido/buck,zpao/buck,artiya4u/buck,shybovycha/buck,stuhood/buck,rowillia/buck,romanoid/buck,justinmuller/buck,tgummerer/buck,rmaz/buck,facebook/buck,dsyang/buck,Learn-Android-app/buck,janicduplessis/buck,k21/buck,liuyang-li/buck,raviagarwal7/buck,bocon13/buck,sdwilsh/buck,OkBuilds/buck,stuhood/buck,romanoid/buck,clonetwin26/buck,nguyentruongtho/buck,zhan-xiong/buck,mikekap/buck,darkforestzero/buck,bocon13/buck,Dominator008/buck,rmaz/buck,SeleniumHQ/buck