MachinerSuite.TestMachinerMachineAssignedUnits agent should be terminated

[Curtis Hovey]

As seen at
    http://reports.vapour.ws/releases/issue/57addf95749a560da2ce4fc8

machiner_test.go:182:
    // If EnsureDead fails with "machine has assigned units", then
    // the worker will not fail, but will wait for more events.
    c.Check(err, jc.ErrorIsNil)
... value *errors.Err = &errors.Err{message:"agent should be terminated", cause:error(nil), previous:error(nil), file:"github.com/juju/juju/worker/errors.go", line:20} ("agent should be terminated")
... error stack:
 github.com/juju/juju/worker/errors.go:20: agent should be terminated