toolsSuite.SetUpTest invalid version on windows

[Curtis Hovey]

As seen in
    http://reports.vapour.ws/releases/issue/566c335d749a560b0c88e1d6
and specifically
    http://reports.vapour.ws/releases/3424/job/run-unit-tests-win2012-amd64/attempt/1711

We can see a ridiculous error
tools_test.go:39:
    s.AddDefaultToolsToState(c)
c:/users/admini~1/appdata/local/temp/tmpmkx7ti/gogo/src/github.com/juju/juju/juju/testing/conn.go:309:
    c.Assert(err, jc.ErrorIsNil)
... value *errors.Err = &errors.Err{message:"invalid tools version", cause:(*errors.Err)(0xc0848ac6e0), previous:(*errors.Err)(0xc0848ac6e0), file:"github.com/juju/juju/state/toolstorage/tools.go", line:52} ("invalid tools version: version \"1.25.2-trusty-amd64\" != \"1.25.2-trusty-amd64\"")

The issue is consistently seen on in the windows unit tests in 1.25 after commit
    https://github.com/juju/juju/commit/127742f9b6d109ba219dc3cd92d6eaed82bf508a
But the issue ha a longer history.

I suspect that there is a timing issue with the test, The version was invalid when the error was raised, but the value became valid at the time of printing.