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.
And before you say it, I fully agree that Before should happen before After (for flow reasons). Since this is not the only example and this patch is not fixing it as a whole, best to leave where it is for now and move that to a different PR.