test/random.jl: segregate deterministic tests at the end

See https://github.com/JuliaLang/julia/issues/8313 for context and in particular https://github.com/JuliaLang/julia/issues/8313#issuecomment-55493151 for the rationale of this change.
In short, the first test in "test/random.jl", which needed to seed the global RNG with a deterministic value (`srand(0)`), was leaking determinism on all the tests coming after it.