Machine agent is uninstalled even when "uninstall-agent" file does not exist.

[Eric Snow]

(related: lp:1514874, lp:1464304, lp:1580221, lp:1580231)

The code in lp:1464304 introduced the "uninstall-agent" file to indicate that the machine is dead and agent may be uninstalled. On 1.25 the check for this file appears to work correctly but the agent is uninstalled anyway. Using the local provider:

1) Modify the apipassword on the /var/lib/juju/agents/machine-1/agent.conf
2) Restart jujud-machine-1 (e.g. "juju ssh 0 reboot now").

2016-05-03 15:32:31 ERROR juju.worker.apicaller open.go:169 agent terminating due to error returned during API open: invalid entity name or password
2016-05-03 15:32:31 INFO juju.worker runner.go:275 stopped "api", err: agent should be terminated
2016-05-03 15:32:31 DEBUG juju.worker runner.go:203 "api" done: agent should be terminated
2016-05-03 15:32:31 ERROR juju.worker runner.go:212 fatal "api": agent should be terminated
2016-05-03 15:32:31 DEBUG juju.worker runner.go:248 killing "statestarter"
2016-05-03 15:32:31 DEBUG juju.worker runner.go:248 killing "termination"
2016-05-03 15:32:31 INFO juju.worker runner.go:275 stopped "statestarter", err: <nil>
2016-05-03 15:32:31 INFO juju.worker runner.go:275 stopped "termination", err: <nil>
2016-05-03 15:32:31 DEBUG juju.worker runner.go:203 "statestarter" done: <nil>
2016-05-03 15:32:31 DEBUG juju.worker runner.go:227 no restart, removing "statestarter" from known workers
2016-05-03 15:32:31 DEBUG juju.worker runner.go:203 "termination" done: <nil>
2016-05-03 15:32:31 DEBUG juju.worker runner.go:227 no restart, removing "termination" from known workers
2016-05-03 15:32:31 DEBUG juju.cmd.jujud machine.go:1741 uninstall file "/var/lib/juju/uninstall-agent" does not exist
2016-05-03 15:32:31 INFO juju.cmd supercommand.go:435 command finished