Ephemeral data port

Made it so that master and worker supports ephemeral ports (aka, system finds a free port).  Was going to add data port config, but turns out that `tachyon.worker.data.port` was already set for this.  

I want to clean up the patch a bit more, so shouldn't be merged yet.  Also, this patch won't be enough to make tests run concurrently (need a thread-safe/ isolated config).
java convention.  If your class is only there to host static methods, then its good to make constructor private so no one can create an instance of the class.  Its unrelated to this patch so could remove.