Add support for /etc/buckconfig and /etc/buckconfig.d.
Add support for /etc/buckconfig and /etc/buckconfig.d.

Summary: More levels of configuration is lame, but sometimes necessary to configure Buck for all users.

Test Plan: Test locally, /etc/buckconfig is loaded.

tgummerer/buck,stuhood/buck,marcinkwiatkowski/buck,Heart2009/buck,liuyang-li/buck,brettwooldridge/buck,tgummerer/buck,Distrotech/buck,dpursehouse/buck,justinmuller/buck,pwz3n0/buck,raviagarwal7/buck,brettwooldridge/buck,OkBuilds/buck,rowillia/buck,rowillia/buck,shybovycha/buck,davido/buck,LegNeato/buck,artiya4u/buck,ilya-klyuchnikov/buck,neonichu/buck,artiya4u/buck,artiya4u/buck,justinmuller/buck,illicitonion/buck,mogers/buck,JoelMarcey/buck,illicitonion/buck,neonichu/buck,grumpyjames/buck,OkBuilds/buck,robbertvanginkel/buck,pwz3n0/buck,justinmuller/buck,mikekap/buck,zhuxiaohao/buck,JoelMarcey/buck,davido/buck,siddhartharay007/buck,SeleniumHQ/buck,zpao/buck,OkBuilds/buck,mikekap/buck,shs96c/buck,clonetwin26/buck,rmaz/buck,Heart2009/buck,darkforestzero/buck,LegNeato/buck,vschs007/buck,zhuxiaohao/buck,JoelMarcey/buck,raviagarwal7/buck,davido/buck,mikekap/buck,vschs007/buck,Dominator008/buck,clonetwin26/buck,clonetwin26/buck,Learn-Android-app/buck,k21/buck,OkBuilds/buck,clonetwin26/buck,romanoid/buck,OkBuilds/buck,Learn-Android-app/buck,Distrotech/buck,kageiit/buck,sdwilsh/buck,vine/buck,mikekap/buck,ilya-klyuchnikov/buck,1yvT0s/buck,Heart2009/buck,dsyang/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,k21/buck,1yvT0s/buck,lukw00/buck,pwz3n0/buck,Addepar/buck,raviagarwal7/buck,liuyang-li/buck,zpao/buck,mikekap/buck,SeleniumHQ/buck,illicitonion/buck,siddhartharay007/buck,mnuessler/buck,mnuessler/buck,facebook/buck,janicduplessis/buck,daedric/buck,tgummerer/buck,siddhartharay007/buck,marcinkwiatkowski/buck,Dominator008/buck,sdwilsh/buck,siddhartharay007/buck,raviagarwal7/buck,robbertvanginkel/buck,Addepar/buck,grumpyjames/buck,daedric/buck,facebook/buck,Heart2009/buck,ilya-klyuchnikov/buck,Dominator008/buck,shs96c/buck,janicduplessis/buck,romanoid/buck,rhencke/buck,zhuxiaohao/buck,shybovycha/buck,grumpyjames/buck,clonetwin26/buck,mogers/buck,illicitonion/buck,artiya4u/buck,Heart2009/buck,janicduplessis/buck,ilya-klyuchnikov/buck,dushmis/buck,vine/buck,davido/buck,davido/buck,LegNeato/buck,rowillia/buck,liuyang-li/buck,janicduplessis/buck,darkforestzero/buck,janicduplessis/buck,sdwilsh/buck,k21/buck,facebook/buck,LegNeato/buck,liuyang-li/buck,Learn-Android-app/buck,dpursehouse/buck,sdwilsh/buck,rmaz/buck,shs96c/buck,luiseduardohdbackup/buck,clonetwin26/buck,vschs007/buck,OkBuilds/buck,zhan-xiong/buck,raviagarwal7/buck,vine/buck,mogers/buck,stuhood/buck,justinmuller/buck,SeleniumHQ/buck,pwz3n0/buck,clonetwin26/buck,Learn-Android-app/buck,daedric/buck,rhencke/buck,justinmuller/buck,tgummerer/buck,rhencke/buck,mikekap/buck,justinmuller/buck,Addepar/buck,vschs007/buck,romanoid/buck,nguyentruongtho/buck,davido/buck,dushmis/buck,luiseduardohdbackup/buck,rowillia/buck,Addepar/buck,SeleniumHQ/buck,Addepar/buck,robbertvanginkel/buck,robbertvanginkel/buck,bocon13/buck,LegNeato/buck,sdwilsh/buck,rowillia/buck,hgl888/buck,lukw00/buck,robbertvanginkel/buck,JoelMarcey/buck,robbertvanginkel/buck,Dominator008/buck,darkforestzero/buck,1yvT0s/buck,facebook/buck,janicduplessis/buck,marcinkwiatkowski/buck,1yvT0s/buck,ilya-klyuchnikov/buck,davido/buck,lukw00/buck,daedric/buck,darkforestzero/buck,shs96c/buck,zhuxiaohao/buck,janicduplessis/buck,clonetwin26/buck,Addepar/buck,robbertvanginkel/buck,tgummerer/buck,shs96c/buck,marcinkwiatkowski/buck,k21/buck,darkforestzero/buck,marcinkwiatkowski/buck,dsyang/buck,tgummerer/buck,zhan-xiong/buck,robbertvanginkel/buck,bocon13/buck,zhan-xiong/buck,davido/buck,sdwilsh/buck,brettwooldridge/buck,robbertvanginkel/buck,romanoid/buck,bocon13/buck,rowillia/buck,ilya-klyuchnikov/buck,vschs007/buck,janicduplessis/buck,shybovycha/buck,bocon13/buck,kageiit/buck,robbertvanginkel/buck,JoelMarcey/buck,Addepar/buck,mogers/buck,zhuxiaohao/buck,sdwilsh/buck,mikekap/buck,kageiit/buck,vine/buck,artiya4u/buck,vschs007/buck,LegNeato/buck,hgl888/buck,dsyang/buck,Learn-Android-app/buck,rowillia/buck,dsyang/buck,daedric/buck,rmaz/buck,JoelMarcey/buck,Addepar/buck,daedric/buck,rmaz/buck,grumpyjames/buck,darkforestzero/buck,janicduplessis/buck,rmaz/buck,grumpyjames/buck,dsyang/buck,Dominator008/buck,Dominator008/buck,neonichu/buck,k21/buck,ilya-klyuchnikov/buck,bocon13/buck,zhan-xiong/buck,liuyang-li/buck,bocon13/buck,liuyang-li/buck,SeleniumHQ/buck,1yvT0s/buck,shs96c/buck,illicitonion/buck,rmaz/buck,dpursehouse/buck,SeleniumHQ/buck,daedric/buck,grumpyjames/buck,luiseduardohdbackup/buck,grumpyjames/buck,brettwooldridge/buck,janicduplessis/buck,daedric/buck,tgummerer/buck,luiseduardohdbackup/buck,stuhood/buck,dpursehouse/buck,rhencke/buck,OkBuilds/buck,romanoid/buck,illicitonion/buck,dsyang/buck,raviagarwal7/buck,sdwilsh/buck,zpao/buck,zpao/buck,nguyentruongtho/buck,illicitonion/buck,marcinkwiatkowski/buck,rowillia/buck,marcinkwiatkowski/buck,sdwilsh/buck,shybovycha/buck,shs96c/buck,ilya-klyuchnikov/buck,rowillia/buck,SeleniumHQ/buck,dpursehouse/buck,vschs007/buck,darkforestzero/buck,sdwilsh/buck,bocon13/buck,rhencke/buck,rmaz/buck,pwz3n0/buck,marcinkwiatkowski/buck,dsyang/buck,ilya-klyuchnikov/buck,rmaz/buck,justinmuller/buck,rmaz/buck,shybovycha/buck,dsyang/buck,brettwooldridge/buck,nguyentruongtho/buck,janicduplessis/buck,1yvT0s/buck,brettwooldridge/buck,mikekap/buck,justinmuller/buck,rhencke/buck,Distrotech/buck,LegNeato/buck,raviagarwal7/buck,clonetwin26/buck,LegNeato/buck,luiseduardohdbackup/buck,hgl888/buck,facebook/buck,mogers/buck,nguyentruongtho/buck,rmaz/buck,mogers/buck,brettwooldridge/buck,shybovycha/buck,robbertvanginkel/buck,robbertvanginkel/buck,zhuxiaohao/buck,pwz3n0/buck,justinmuller/buck,dushmis/buck,pwz3n0/buck,clonetwin26/buck,dushmis/buck,luiseduardohdbackup/buck,stuhood/buck,marcinkwiatkowski/buck,Dominator008/buck,k21/buck,rhencke/buck,grumpyjames/buck,tgummerer/buck,davido/buck,lukw00/buck,artiya4u/buck,siddhartharay007/buck,OkBuilds/buck,dushmis/buck,dushmis/buck,vine/buck,vine/buck,Addepar/buck,nguyentruongtho/buck,brettwooldridge/buck,vschs007/buck,grumpyjames/buck,mogers/buck,stuhood/buck,Distrotech/buck,tgummerer/buck,daedric/buck,mnuessler/buck,neonichu/buck,JoelMarcey/buck,shybovycha/buck,Heart2009/buck,darkforestzero/buck,SeleniumHQ/buck,mogers/buck,lukw00/buck,LegNeato/buck,Distrotech/buck,justinmuller/buck,stuhood/buck,tgummerer/buck,raviagarwal7/buck,Dominator008/buck,LegNeato/buck,hgl888/buck,zpao/buck,zhuxiaohao/buck,Learn-Android-app/buck,k21/buck,neonichu/buck,shybovycha/buck,neonichu/buck,dsyang/buck,pwz3n0/buck,raviagarwal7/buck,vine/buck,OkBuilds/buck,mnuessler/buck,k21/buck,dsyang/buck,kageiit/buck,shs96c/buck,liuyang-li/buck,mogers/buck,mikekap/buck,LegNeato/buck,lukw00/buck,pwz3n0/buck,k21/buck,stuhood/buck,k21/buck,ilya-klyuchnikov/buck,Distrotech/buck,stuhood/buck,facebook/buck,OkBuilds/buck,zhan-xiong/buck,rmaz/buck,zhuxiaohao/buck,Addepar/buck,liuyang-li/buck,romanoid/buck,darkforestzero/buck,JoelMarcey/buck,zhan-xiong/buck,rhencke/buck,brettwooldridge/buck,mnuessler/buck,nguyentruongtho/buck,rhencke/buck,shybovycha/buck,daedric/buck,illicitonion/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,rowillia/buck,dpursehouse/buck,davido/buck,illicitonion/buck,rmaz/buck,clonetwin26/buck,vine/buck,grumpyjames/buck,illicitonion/buck,k21/buck,JoelMarcey/buck,dushmis/buck,zhuxiaohao/buck,mikekap/buck,lukw00/buck,rmaz/buck,bocon13/buck,Dominator008/buck,zpao/buck,davido/buck,Distrotech/buck,dushmis/buck,raviagarwal7/buck,JoelMarcey/buck,hgl888/buck,sdwilsh/buck,brettwooldridge/buck,neonichu/buck,illicitonion/buck,hgl888/buck,sdwilsh/buck,zhan-xiong/buck,vschs007/buck,zhan-xiong/buck,lukw00/buck,kageiit/buck,neonichu/buck,illicitonion/buck,zhan-xiong/buck,1yvT0s/buck,marcinkwiatkowski/buck,LegNeato/buck,mnuessler/buck,darkforestzero/buck,janicduplessis/buck,lukw00/buck,JoelMarcey/buck,shybovycha/buck,brettwooldridge/buck,Learn-Android-app/buck,rowillia/buck,shs96c/buck,artiya4u/buck,vschs007/buck,hgl888/buck,darkforestzero/buck,Addepar/buck,marcinkwiatkowski/buck,Heart2009/buck,romanoid/buck,vine/buck,OkBuilds/buck,facebook/buck,brettwooldridge/buck,OkBuilds/buck,Dominator008/buck,Learn-Android-app/buck,stuhood/buck,rhencke/buck,bocon13/buck,OkBuilds/buck,k21/buck,luiseduardohdbackup/buck,dpursehouse/buck,mikekap/buck,SeleniumHQ/buck,1yvT0s/buck,romanoid/buck,clonetwin26/buck,siddhartharay007/buck,shybovycha/buck,hgl888/buck,justinmuller/buck,bocon13/buck,siddhartharay007/buck,mikekap/buck,zhan-xiong/buck,Heart2009/buck,lukw00/buck,artiya4u/buck,vschs007/buck,shs96c/buck,JoelMarcey/buck,kageiit/buck,luiseduardohdbackup/buck,raviagarwal7/buck,liuyang-li/buck,kageiit/buck,mogers/buck,dushmis/buck,LegNeato/buck,bocon13/buck,justinmuller/buck,grumpyjames/buck,artiya4u/buck,mnuessler/buck,brettwooldridge/buck,vine/buck,zpao/buck,Addepar/buck,darkforestzero/buck,SeleniumHQ/buck,Learn-Android-app/buck,shs96c/buck,davido/buck,dpursehouse/buck,darkforestzero/buck,JoelMarcey/buck,dsyang/buck,dsyang/buck,mogers/buck,dushmis/buck,bocon13/buck,Dominator008/buck,SeleniumHQ/buck,Addepar/buck,SeleniumHQ/buck,Learn-Android-app/buck,liuyang-li/buck,1yvT0s/buck,davido/buck,zhan-xiong/buck,vschs007/buck,stuhood/buck,ilya-klyuchnikov/buck,mnuessler/buck,daedric/buck,siddhartharay007/buck,grumpyjames/buck,romanoid/buck,vschs007/buck,shybovycha/buck,luiseduardohdbackup/buck,zhan-xiong/buck,romanoid/buck,Learn-Android-app/buck,romanoid/buck,rowillia/buck,romanoid/buck,hgl888/buck,tgummerer/buck,Distrotech/buck,raviagarwal7/buck,liuyang-li/buck,neonichu/buck,mnuessler/buck,illicitonion/buck,Heart2009/buck,pwz3n0/buck,lukw00/buck,artiya4u/buck,Dominator008/buck,romanoid/buck,pwz3n0/buck,dsyang/buck,nguyentruongtho/buck,justinmuller/buck,k21/buck,raviagarwal7/buck,shs96c/buck,shybovycha/buck,marcinkwiatkowski/buck,Distrotech/buck,vine/buck,zhan-xiong/buck,clonetwin26/buck,shs96c/buck,rhencke/buck,daedric/buck,stuhood/buck,sdwilsh/buck,artiya4u/buck,daedric/buck,Distrotech/buck,Distrotech/buck,siddhartharay007/buck