[Tachyon-14] TachyonURI (Hadoop)

Refactor hadoop underfs interface and util methods to use Tachyon URI.
We seem to have 2 different conventions, using cPath for the hadoop path and then path for the Tachyon path or using path for the hadoop path and using tPath for the tachyon path. I can refactor some more to make it consistent throughout the file. Which would be preferred? Personally I would go with cPath.