use latest 3dt
use latest 3dt

Use history service to retrieve a list of agents if leader.mesos dns record
is not available.
https://github.com/dcos/3dt/pull/16
DCOS-6435

darkonie/dcos,asridharan/dcos,surdy/dcos,jeid64/dcos,mnaboka/dcos,mesosphere-mergebot/dcos,BenWhitehead/dcos,mnaboka/dcos,kensipe/dcos,mellenburg/dcos,mesosphere-mergebot/dcos,dcos/dcos,dcos/dcos,branden/dcos,surdy/dcos,mnaboka/dcos,xinxian0458/dcos,BenWhitehead/dcos,mnaboka/dcos,vishnu2kmohan/dcos,darkonie/dcos,mellenburg/dcos,lingmann/dcos,mellenburg/dcos,dcos/dcos,kensipe/dcos,GoelDeepak/dcos,amitaekbote/dcos,mellenburg/dcos,mesosphere-mergebot/mergebot-test-dcos,lingmann/dcos,mesosphere-mergebot/mergebot-test-dcos,jeid64/dcos,GoelDeepak/dcos,branden/dcos,branden/dcos,BenWhitehead/dcos,GoelDeepak/dcos,GoelDeepak/dcos,amitaekbote/dcos,kensipe/dcos,amitaekbote/dcos,surdy/dcos,xinxian0458/dcos,lingmann/dcos,xinxian0458/dcos,darkonie/dcos,jeid64/dcos,mesosphere-mergebot/dcos,jeid64/dcos,asridharan/dcos,surdy/dcos,darkonie/dcos,darkonie/dcos,kensipe/dcos,amitaekbote/dcos,vishnu2kmohan/dcos,dcos/dcos,lingmann/dcos,mesosphere-mergebot/mergebot-test-dcos,xinxian0458/dcos,asridharan/dcos,vishnu2kmohan/dcos,asridharan/dcos,branden/dcos,mesosphere-mergebot/dcos,dcos/dcos,mesosphere-mergebot/mergebot-test-dcos,BenWhitehead/dcos,vishnu2kmohan/dcos,mnaboka/dcos