Added a list of "unreachable" agents to the registry.
Added a list of "unreachable" agents to the registry.

These are agents that have failed health checks.

Review: https://reviews.apache.org/r/50700/

dforsyth/mesos,chhsia0/mesos,asamerh4/mesos,verizonlabs/mesos,neilconway/mesos,jpeach/mesos,dforsyth/mesos,neilconway/mesos,zmalik/mesos,Gilbert88/mesos,reneploetz/mesos,asamerh4/mesos,craimbert/mesos,Gilbert88/mesos,jpeach/mesos,reneploetz/mesos,verizonlabs/mesos,verizonlabs/mesos,Gilbert88/mesos,craimbert/mesos,yuquanshan/customizedMesos,kaysoky/mesos,verizonlabs/mesos,reneploetz/mesos,Aman-Jain-14/customizedMesos,abudnik/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,zmalik/mesos,chhsia0/mesos,andschwa/mesos,gsantovena/mesos,yuquanshan/customizedMesos,abudnik/mesos,dforsyth/mesos,dforsyth/mesos,zmalik/mesos,abudnik/mesos,yuquanshan/customizedMesos,andschwa/mesos,kaysoky/mesos,asamerh4/mesos,Gilbert88/mesos,yuquanshan/customizedMesos,asamerh4/mesos,chhsia0/mesos,reneploetz/mesos,andschwa/mesos,reneploetz/mesos,yuquanshan/customizedMesos,Gilbert88/mesos,kaysoky/mesos,neilconway/mesos,gsantovena/mesos,kaysoky/mesos,neilconway/mesos,craimbert/mesos,andschwa/mesos,gsantovena/mesos,kaysoky/mesos,Aman-Jain-14/customizedMesos,craimbert/mesos,dforsyth/mesos,gsantovena/mesos,yuquanshan/customizedMesos,abudnik/mesos,Aman-Jain-14/customizedMesos,asamerh4/mesos,zmalik/mesos,chhsia0/mesos,jpeach/mesos,neilconway/mesos,craimbert/mesos,Aman-Jain-14/customizedMesos,gsantovena/mesos,jpeach/mesos,verizonlabs/mesos,craimbert/mesos,neilconway/mesos,reneploetz/mesos,andschwa/mesos,gsantovena/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,zmalik/mesos,abudnik/mesos,chhsia0/mesos,abudnik/mesos,craimbert/mesos,chhsia0/mesos,reneploetz/mesos,jpeach/mesos,jpeach/mesos,asamerh4/mesos,verizonlabs/mesos,gsantovena/mesos,dforsyth/mesos,neilconway/mesos,Gilbert88/mesos,abudnik/mesos,kaysoky/mesos,andschwa/mesos,Gilbert88/mesos,jpeach/mesos,Aman-Jain-14/customizedMesos,andschwa/mesos,kaysoky/mesos,chhsia0/mesos,asamerh4/mesos,zmalik/mesos,verizonlabs/mesos,zmalik/mesos