Patch for JIRA KNOX-58

[Dilli Arumugam]

Hi Kevin,
I am attaching the patch for  fixing Knox JIra issue
           https://issues.apache.org/jira/browse/KNOX-58

NameNode endpoint exposed to gateway clients in runtime exception

Would you commit this if it looks fine?
Please let me know if I have to rework the fix.

Thanks.
Dilli