TestDyingMachine fails when unit agent is running on machine

Tests on go-bot are failing in cmd/jujud/machine_test.go on the MachineSuite.TestDyingMachine case.

Somehow the deployer in the test getting at the unit-agent running on the machine and trying to interact with it:

[LOG] 19.19979 INFO juju.worker.deployer checking unit "tarmac/0"
[LOG] 19.20017 DEBUG juju rpc/jsoncodec: <- {"RequestId":8,"Type":"Deployer","Request":"Life","Params":{"Entities":[{"Tag":"unit-tarmac-0"}]}}
[LOG] 19.20024 DEBUG juju rpc/jsoncodec: <- {"RequestId":9,"Type":"StringsWatcher","Id":"2","Request":"Next","Params":{}}
[LOG] 19.20256 DEBUG juju rpc/jsoncodec: -> {"RequestId":8,"Response":{"Results":[{"Life":"","Error":{"Message":"permission denied","Code":"unauthorized access"}}]}}
[LOG] 19.20282 INFO juju.worker.deployer recalling unit "tarmac/0"
[LOG] 19.20390 ERROR juju worker: fatal "deployer": remove /etc/init/jujud-machine-3:unit-tarmac-0.conf: permission denied

For the full log, see:

<https://code.launchpad.net/~gz/juju-core/itsy_bitsy_change/+merge/177424/comments/399449/+download>