Test utils need to be more modular

[gideonthomas]

With the new redis patch, tests/lib/util.js relies on a redis server as it starts a server every time it is required in. However, there are several methods inside util.js such as ensureFileSystem, etc. that do not need the redis server running to be used.

It is probably a good idea to rip this code and those alike from util.js and put them in a separate file so that we don't always need redis to run tests that don't really need them. Then we can just require these new files into these kind of tests and into util.js to be used as needed.