TACHYON-198 Move UserConf usage to use TachyonConf

This PR consist next steps to integrate new configuration work:
-) Remove usage of UserConf
-) Push TachyonConf to Tachyon Hadoop's file system (aka TFS class).
-) Remove UserConf.java from repo.
From a new readers perspective, the name is very weird. I don't think you added it with this patch, but I think that this should be addressed before going to master. Concerned that this makes the code less readable.