statusSuite.SetUpTest cannot read controller kontroll: timeout acquiring mutex

[Curtis Hovey]

As seen at
    http://reports.vapour.ws/releases/issue/58cf6709749a5675eb3ab6ec

/home/ubuntu/juju-core_2.2-beta1/src/github.com/juju/juju/juju/testing/conn.go:341:
    c.Assert(err, jc.ErrorIsNil)
... value *errors.Err = &errors.Err{message:"error reading controller \"kontroll\" info", cause:(*errors.Err)(0x4820235810), previous:(*errors.Err)(0x48204331d0), file:"github.com/juju/juju/environs/bootstrap/prepare.go", line:84} ("error reading controller \"kontroll\" info: cannot read controller kontroll: timeout acquiring mutex")
... error stack:
 github.com/juju/mutex/errors.go:11: timeout acquiring mutex
 github.com/juju/juju/jujuclient/file.go:53:
 github.com/juju/juju/jujuclient/file.go:97: cannot read controller kontroll
 github.com/juju/juju/environs/bootstrap/prepare.go:84: error reading controller "kontroll" info