TACHYON-71 Prevent Thrift exception from leaking out from MasterClient and WorkerClient classes.

Remove invalid JavaDoc "@throws TException" in method declaration.
Prevent leaking of Thrift exceptions (TException and its inheritance classes) to outside of MasterClient and WorkerClient classes because no
classes outside MasterClient and WorkerClient should know about Thrift services.
Small cleanup to remove empty finally clause in TFsShell class.
We could do that but all the other methods that try to get and Id catch the TException and just return -1. 
For this patch, I am following that pattern. We could address the behavior with different PR I suppose.