I'm a little confused on why we are specifying root-level directories to use within Tachyon? Perhaps I am misunderstanding the intention of this code, but it looks like tachyonStorePath will look something like "/tmp/spark-aef88fef89ea/2", but that this will not be a path in the root file system, but rather within Tachyon itself -- i.e., we are referring to the URI `tachyon://localhost:19998/tmp/spark-aef88fef89ea/2`.

I suppose this makes sense, it's just really weird to use the java.io.tmpdir to refer to a path within Tachyon, when it is really referring to a path in the rootfs of the current system. Is this path actually going to be stored in the rootfs, or within Tachyon itself?