Make fest-util a test only dependency

With the latest versions of fest-assert-1.x, fest-reflect exists a version skew with the latest version of fest-util (1.2.5).

Robolectric depending upon fest-util 1.2.5 breaks dependent projects that have a dependency on fest-assert-1.x / fest-reflect because fest-assert depends on methods removed from the version of fest-util that Robolectric depends upon.

I recommend that Robolectric not include fest-util as a production dependency (test scoped is fine) because fest-util is a dangerous library to include transitively.