MachineSuite.TestUpgradeRequest timed out waiting for agent to finish

[Curtis Hovey]

As seen in
    http://reports.vapour.ws/releases/issue/585d3ed2749a5615728e56c3

machine_test.go:536:
    s.testUpgradeRequest(c, a, m.Tag().String(), currentTools)
/home/ubuntu/juju-core_2.1-rc1/src/github.com/juju/juju/environs/testing/tools.go:117:
    c.Assert(obtained, gc.FitsTypeOf, &upgrader.UpgradeReadyError{})
... obtained *errors.errorString = &errors.errorString{s:"timed out waiting for agent to finish; stop error: <nil>"} ("timed out waiting for agent to finish; stop error: <nil>")

[Anastasia (anastasia-macmood)]

This failure looks to have been fixed as I cannot make this test to fail locally and under stress.