Ensure that root of generated Cells is absolute.
Ensure that root of generated Cells is absolute.

Summary:
Also catches a problem when figuring out which build file to
parse.

Test Plan: buck test --all

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