Fixed TACHYON-97

Current implementation of read(long position, byte[] buffer, int offset, int length) in HdfsFileInputStream is incomplete: 
1. It does not consider the boundary of file length, which could lead to an out of range issue when seeking the requested position in bytebuffer. 
2. It does not recover the original offset after function call.
Hard coding Tachyon scheme in core-site.xml does not solve this issue (at least for my recent tests). However, I haven't seen any downside issue after removing this statement so far. In addition, all unit tests can run smoothly without this statement.