Helper methods for creating multi-project tests

I really don't like this approach. It's tying together the IntegrateSpec and this helper in a weird way. And the act of taking a list of subprojects is awkward to call. I really would have prefered a simple "addSubproject" call that takes the project name, and the build file, and returns the directory of the project. Specifying a build file is extremely common in this usage, and having to pull it out of the map makes it harder than it needs to be.