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.
since you keep doing this, would be good to add a small helper method in this class that makes this cleaner.

```java
private WriteType getWriteType() {
  return mTachyonConf.getEnum(Constants.USER_DEFAULT_WRITE_TYPE, WriteType.CACHE_THROUGH);
}
```