fixed Exception for unknown HiveServer2 security mechanism that otherwis...

...e obscures the real error with global name _ not defined unhandled exception

Best Regards,

Hari Sekhon
Former Clouderan
http://www.linkedin.com/in/harisekhon
How about putting the correct _() around the string to translate?

Exception(_('%s server authentication not supported. Valid are %s.') % (hive_mechanism, HiveServerClient.HS2_MECHANISMS.keys()))