unitSuite.SetUpTest timeout acquiring mutex

[Curtis Hovey]

As seen at
    http://reports.vapour.ws/releases/issue/57bd13d6749a5638f818a04d

unit_test.go:39:
    s.uniterSuite.SetUpTest(c)
/home/ubuntu/juju-core_2.0-beta10/src/github.com/juju/juju/juju/testing/conn.go:331:
    c.Assert(err, jc.ErrorIsNil)
... value *errors.Err = &errors.Err{message:"cannot read controller kontroll", cause:(*errors.Err)(0x48202095e0), previous:(*errors.Err)(0x4820839db0), file:"github.com/juju/juju/jujuclient/file.go", line:95} ("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:51:
 github.com/juju/juju/jujuclient/file.go:95: cannot read controller kontroll

[Tim Penhey (thumper)]

https://github.com/juju/juju/pull/7363