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.
Why should we do this? Shouldn't the user create the config up front and then pass it to the FS? Not clear why we would want to support mutating the config by merging another one in after the fact.  Still not clear in the code that uses this why thats the better way.