Comment 1 for bug 1272520

You didn't provide any sort of logs, so I can't be 100% sure that we had the same problem, but the problem I had was due to the fact that the Jenkins master 'master-relation-changed' hook expects (assumes, rather) that the Jenkins slave 'slave-relation-joined' hook will pass a bunch of information during the 'add-relation' which it will then call the hooks/addnode script with. The problem I encountered is that the Jenkins slave does not set 'slaveaddress' and so it is passed by too 'hooks/addnode' via 'master-relation-changed' as an empty string and causes breakage. Once 'slaveaddress' is properly set by the Jenkins slave in 'slave-relation-joined', this particularly problem goes away.