Better error message when ant fails to compile Buck.
Better error message when ant fails to compile Buck.

Summary:
XCode upgrades require folks to re-accept a license, which causes Buck
to fail to compile if you haven't done so (due to nailgun).  The error
message that we use isn't descriptive enough, so this tries to improve
it slightly.

Test Plan: unit tests

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