Removed unnecessary monkeypatching of __builtin__

Replaced it with explicitly importing the gettext function, which is
significantly more readable.

Change-Id: Ia0a7edcf685fb6e4052a8290367b233169529ab8

swift/common/bench.py

@@ -22,6 +22,7 @@ import signal
 import socket
 import logging
 from contextlib import contextmanager
+from gettext import gettext as _
 from optparse import Values
 
 import eventlet